A lot of manufacturers will allow you to make changes like replace a bunk bed setup with a couch. Or add a drop down bed.
There are lots of new 5th wheel floorplans with setups near what you described.
An option would be to add the couch and then seal the ramp door and cover it on the inside with a decorative covering or drapes.
I always thought of leaving the ramp and use it as an outdoor patio area with a screened tent. The garage area would be setup as a large living room/ media room. I've even seen a double french door added to close off the garage when the ramp is down and being used as a raised patio. They just leave the ramp down at night and the french doors provide security.