On my iPad so can't reference you to a previously posted thread right now - but this is a repeat query where you'll find some great answers if you can search/find it. Short answer for every bed: buy regular fitted bottom sheet and 'tuck', then toss on it a sleeping bag, duvet, sleep sack, etc. on top. Two suggestions - enclose every mattress in a mattress protector (moisture, mites, dust, etc.) AND buy light-weight inexpensive sheets that dry fast ... Preferably in a campground compatible color (beige or brown). Got our mattress enclosures, mattress pads, and sheet sets thru Amazon - bunkhouse and dinette are FULL and master is QUEEN (topper expanded from a short to a regular length). Bottom-line - all RVs are money pits and this is one place you don't need anything "special" or costly! UPDATE: Amazon, Elegant Comfort 1500 thread count, taupe, fitted bottom + top + 2 cases = $27 if full size (same day delivery, no shipping if Prime).
http://smile.amazon.com/s/ref=nb_sb_...t+comfort+sets