It's Not a Truck Cargo Bed Extension
This is the first thing to clear up because the phrase "M1 bed extension" reads two ways. There is no Tune product that extends a truck's cargo bed length (the bracket-and-tailgate style extender for short-bed trucks). The product Tune sells under the "bed extension" name is the King-Size Sliding Bed Extension, an interior sleeping platform extender.
Mechanically, it's an aluminum-extrusion and fiberglass-reinforced bracket that slides out from inside the M1, cantilevering forward over the truck cab. When deployed it adds about 20 inches of sleeping length over the cab roof, taking the standard east-west queen platform (60 by 72 mid-size or 60 by 78 full-size) up to a king-size sleeping area.
The "metal bracket" intuition is correct, but the bracket extends the bed you sleep on, not the bed you put cargo in.
What You Get for $300
The Tune King-Size Sliding Bed Extension product details, verified against Tune's product page:
- Price: $300 (bracket mechanism only, mattress separate)
- Material: Aluminum extrusions and fiberglass-reinforced panels
- Install: Owner-installable
- Lead time: 2-4 weeks to build
- Stays installed when closed: yes (the mattress can remain in place during travel)
- In stock: as of June 2026
Tune doesn't publish a weight figure for the bracket. The ordering guide estimates 5-10 lbs based on owner reports. Add it to your payload budget before committing.
Mid-Size vs Full-Size Dimensions
The extension dimensions match the truck class:
| Truck class | M1 base platform | Extension dimensions | Total deployed |
|---|---|---|---|
| Mid-size (Tacoma, Ranger, Colorado, etc.) | 60 × 72 | 20 × 72 | ~80 × 72 |
| Full-size (Tundra, F-150, Silverado, etc.) | 60 × 78 | 20 × 78 | ~80 × 78 |
The extension width (20") is identical between truck classes. The length difference (72" vs 78") matches the M1's underlying platform difference for mid- vs full-size trucks. A standard king-size mattress is 76 by 80; the extended platform sleeps that comfortably for two adults in either configuration.
Mattress Pairing & Total Cost
The bracket alone is unusable without a mattress extension to bridge the new 20-inch section. Tune sells two HEST mattress extensions sized to match:
| Mattress | Dimensions | Material | Price | For |
|---|---|---|---|---|
| HEST Dually Wide Extension | 20 × 72 | Multi-layer memory foam | $249 | Mid-size trucks |
| HEST Dually Queen Extension | 20 × 78 | Multi-layer memory foam | $289 | Full-size trucks |
Total cost for the complete factory setup:
- Mid-size: $300 (bracket) + $249 (HEST Wide Extension) = $549
- Full-size: $300 (bracket) + $289 (HEST Queen Extension) = $589
One alternative worth knowing about: the ROAM Adventure Co modular pad system chains pieces together to form single, double, triple, or quad-width sleeping surfaces. For owners who want a mattress that also works in a tent or van, ROAM's approach is the modular workaround to buying a dedicated extension mattress.
Solo or Couple? The Real Decision
The honest version of this decision, from an active M1 owner posting in the community group:
"I bought the king bed extension for when my partner camps with me. He rarely goes with me so the extension is just mostly in the way. I was wondering if it would safely sit on the bedrail of the Tune and I could just use it as seating."
That's the buying signal. The standard east-west queen platform (60 by 72 mid-size, 60 by 78 full-size) is already oversized for one sleeper. The extension solves a couples problem and a tall-sleeper problem, not a solo problem.
When the extension is worth it:
- You camp with a partner most trips, and the extra width matters for sleep quality
- You're 6 feet or taller, and you want to sleep diagonally for more length (the extension gives you the room to angle)
- You add a kid or pet to the bed regularly
- You're full-timing or extended-camping where sleep comfort compounds
When the extension is usually not worth it:
- You camp solo most of the time, and the bracket spends most nights folded
- You're tight on payload, and the 5-10 lbs plus the mattress weight is competing with battery or water
- You're trying to keep the build under $13,500 all-in for resale or budget reasons
The Mattress-Slide Gap Issue (Worth Knowing Before Ordering)
One real issue surfaces consistently across M1 owner reports. Per the M1 common issues page, owners using the HEST Dually Wide mattress with the King Slide extension report the extension piece sliding overnight, creating an uncomfortable gap between the main mattress and the extension. The included buckle straps help but don't fully prevent movement during sleep, especially for restless sleepers.
Workarounds owners have tried:
- Non-slip rug mat under the mattress. Cuts the slip but adds bulk during stow-and-go.
- Tighter strap tensioning. Partial improvement but the straps can dig into the foam.
- Velcro-loop strips between mattress and platform. A few owners report this fully solves the gap, at the cost of permanent velcro on the platform.
- Living with it. Some sleepers don't move enough overnight for the gap to develop.
This is a real issue, not a dealbreaker. Worth knowing before you commit $549 to the upgrade and discover it on trip one.
For the broader factory configuration discussion (what's worth ordering vs DIY, the full add-on list), see the M1 ordering guide. For mattress alternatives beyond HEST, see the mattress guide.
Order-Time vs Retrofit
The King-Size Sliding Bed Extension is owner-installable per Tune's product page, with a 2-4 week build lead time. Two paths for adding it to your build:
- Order at configuration time. The cleanest path. Tune integrates the bracket into the camper during the build and you receive a finished, ready-to-use system. Most owners go this route.
- Retrofit later. Possible because the bracket is owner-installable, but you'll need to plan for the lead time and the install effort. Order the bracket from Tune, wait the 2-4 weeks, then plan a few hours to install. If you already have the camper, this is the path.
The retrofit option is what makes this a different decision from some Tune factory upgrades (like the MaxxAir fan) where Tune has to cut openings during the build. The bed extension can be added after the fact if you change your mind.
Where to Buy
Tune Outdoor direct, only. The bracket is an OEM Tune product not resold through dealers like R4T or AV Overland Supply, at least as of June 2026.
- Tune Outdoor — King-Size Sliding Bed Extension ($300, the bracket itself)
- Tune Outdoor — HEST Dually Wide Extension (20 × 72) ($249, mid-size mattress)
- Tune Outdoor — HEST Dually Queen Extension (20 × 78) ($289, full-size mattress)
Bed Extension FAQ
What is the Tune M1 bed extension?
The interior sleeping platform extension, not a truck cargo bed extension. A $300 sliding aluminum bracket that pulls out over the truck cab to extend the standard queen sleeping platform to king-size.
How much does the full setup cost?
$549 for mid-size trucks ($300 bracket + $249 HEST Dually Wide Extension) or $589 for full-size trucks ($300 bracket + $289 HEST Dually Queen Extension).
Mid-size vs full-size dimensions?
Mid-size trucks get a 20 × 72 extension. Full-size trucks get a 20 × 78 extension. Total deployed sleeping platform is ~80 × 72 (mid) or ~80 × 78 (full).
Is it worth it for solo camping?
Usually not. The standard queen platform is oversized for one sleeper. The extension solves a couples problem (and a tall-sleeper problem) more than a solo problem. One community quote: "He rarely goes with me so the extension is just mostly in the way."
Can the king mattress stay installed when the camper is closed?
Yes. Both the standard queen platform and the king extension keep their mattresses in place during travel. Open the pop-top and the bed is ready to use.
Does the bed extension have any known issues?
One real issue: the HEST Dually Wide mattress paired with the extension can slide overnight, creating a gap. Buckle straps help but don't fully prevent it. Workarounds include non-slip mats, tighter straps, or velcro-loop strips. See the common issues page for the full discussion.
Order-time or retrofit?
Both work. The bracket is owner-installable with a 2-4 week build lead time. Most owners order at configuration time for the clean integration. Retrofit is possible if you change your mind later.
Add it to the payload math before you commit
The bracket (~5-10 lbs) plus the HEST mattress extension (~5-8 lbs) is real weight high in the camper. Open the payload calculator, add both components, and check headroom before adding $549 worth of upgrade to your order.