Here's a little project I completed recently. It was at my wife's behest to provide additional sleeping space for grandchildren. First I removed a bottom cabinet on the curb side of my 33' Argosy.
Then I built a folding bench-bed that went along the wall.
When open it is just about the right size for a twin mattress.
Altogether the project involved about 12 hours of labor, some red oak 1x3s, one sheet of 3/4" maple cabinet veneer on sale from Home Depot, and a small piece of oak veneer. I moved the cabinet doors to the new bench to close it up when folded. The project turned out to be easier than I thought it might be and looked better than I thought I could make it.