What do most people use for bedding in travel trailers where the bed is the daytime dining table?
Same as at home. A quilted mattress pad, a set of double bed sheets (tucking the extra length of the fitted sheet under a few inches) and pillows and a down comforter. The comforter can be stuffed into a pillow case and stuck in a cabinet during the day, along with the sheets. I made sham covers for the pillows that match the trailer upholstery so they can be used as throw pillows on the couch at the other end of the trailer during the daytime.
The sheet sets sold for truckers (in large truck stop stores) are the correct width, but far too long. Most people use the dinette for sleeping rarely, so use double-bed sheets tucked under. Even single bed sheets will work, since the dinette is not wide. Some department stores sell elastic clips that attach to the corners to keep the sheets snug - they are are a really handy thing to use, if you can find them. In other words - use what you have! The main problem with any travel trailer is always storage - where to pack the sheets during the day.
Pillows sheet light blanket if hot a sleeping bag when its cool at night. Its all easily rolled up stashed away
regular bedding. we just fold it up and store it when its a table.