- Hybrid
- 13.25 in thick
- Soft / Medium / Firm
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That's an RV king, 6 in narrower than a regular king (76 × 80 in). A regular king won't fit, so get an RV king in exactly 70 × 80 in.
About the RV king size →Keystone 2018 brochure, 2018.
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The Alpine bedroom. Measure the platform, not the old mattress, before you buy.
| Year | Main bed | Bunks | Other beds | Source |
|---|---|---|---|---|
| 2017 | 70 × 80 in King | – | – | Keystone spec sheet |
| 2018 | 70 × 80 in King | – | – | Keystone 2018 brochure |
Years not listed weren't published.

Keystone's 2017 3501RL floorplan.
Check the year and length against your RV before you order.
| Year | Model | Length | Sleeps |
|---|---|---|---|
| 2017 | Alpine 3501RL | 39' 0" | – |
The main bed is 70 × 80 in (Keystone 2018 brochure, 2018).