It would not be difficult to add a door. My 34fk has the optional door on the right side about 1 footfrom the tailgate. Just do what that plant does, cut a hole the proper size and screw it in, just like the existing kitchen door. This procedure applies to the models (25' and up) that have walls made of FRP plywood. Not the smaller ultralite units that have a different wall construction.
I added a second window to front bedroom. You may want to consider adding the alluminum square stock inside the perimeter of the opening like the factory does to strengthen it
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2013 Ultra work and play 275ULSBS
Towed by 98 2500 Dodge Cummins hand built by me
Polaris RZR couple of Ski Doo REVs