What possible reason would u have for a second shower i just noticed u want 2 FULL baths. Comeone
But here is another plan. Get that Marathon u like. Be sure it has OTR AC no slides.
Get it with 1 couch and chairs other side and if u could find it with table and chairs no booth even better but most marathon i can recall have booths.
So empty the livingroom and kitchen furnature. Couch tables chairs booth all. Save it Disassemble corectly.
Directly behind the driver put a water closet with a toilet and sink. The water supply and drain simple right down the wall to the plumbing bay and through the floor drivers side where u dump already. Then fill the rest of the space with nice captians chairs thst recline footrests top shelf chairs. some flip out tables on them. u could fit plenty easy. Say maybe 3 across with a good isle maybe 4 across and comfortable with really nice captians chairs. They could be fitted with seat belts all of them. Then pull the bed same thing or do a lounge wrap around couch with table or something back there. Same thing save everything removed.
U retain the original full bath and When u were done with it it could be almost put back if the next guy wanted.