Well I was kind of blending two different things.
For the v-berth (permanent, v-shaped bed), I sewed a slipcover that wrapped around like a bottom sheet. Actually, "slipcover" really glorifies it, as it was not all that fancy. But with the V shape you have to make your own, pretty much.
In the main cabin there were two single "settees" which are set up like the beds in your camper. Those cushions were upholstered in a nice fabric by someone else. On those we used fleece "bottom sheets." Mine was actually a fleece, rectangular "sleeping bag" that I used without unzipping it (so it was double thick); my bud's was just a piece of fleece, cut roughly to shape. These were just used for sleeping, so shifting around wasn't an issue. For daytime I just "flip folded" from foot up to head with the pillow right inside and then placed the "square" of bedding in the throw pillow cover.
I used to have the name of a place in Canada that
sold surplus auto seatcover material at a very good price (the velour type stuff). That makes great upholstery as it is very tough yet comfortable.
Raya