Why make up a corner bed at all?
Put a colored coordinated fitted mattress cover (that matches the rest of the RV's interior material) made of heavy material on the mattress and leave it on permanently.
Buy a 2 inch foam topper for the mattress. Use a fitted cotton cover for the foam that zips onto the foam along three sides. Easily unzip and wash this foam cover as often as you want. Sleep directly on this cotton foam cover with sheets, blankets, sleeping bags, etc., on top of the the cotton foam cover and on top of you.
A piece of cake ... this is how we "make up" our RV's corner bed! It's sure nice having a full sized bed always available to flop down on in just a small RV.