Not sure on where to buy the furniture but it is a DIY project. The dinette removal is as easy as unscrewing and pulling staples in the wood that make the seats. If you have an oscillating tool, that will help with a clean removal process.
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2017 Forest River Surveyor 247BHDS...
...Tugged by a 2016 F250 XLT FX4 SuperCrew, Shortbed 6.2L, 4wd, 3.73...
...Joined with a Husky Centerline TS 800-1200lbs WDH
I haven't done but check out company called "recpro rv furniture".
I have seen several videos on YouTube where RVers have replaced their furniture from there.
Good luck. Let me know how you make out. I would like to replace my trifold couch with something with a higher back.
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2017 Forest River Surveyor 251rks
2022 Chevy 3500HD High Country