It isn't hard to do a straight seam on a sewing machine - that's all you'd need to do....
if you want 'fitted' sheets - go to walMart and buy 2 flat sheets and sew around 3 sides to make a big 'pillowcase' to slide the mattress into. if you want the top sheet attached at the bottom sheet, simply sew it on across the bottom. Total cost will be WAY less than those 'camper' sheets, and you'll probably have nicer sheets, too.
I have a 'pocket sheet' set like this that was made for my camper beds - it came with the camper when I bought it, obviously something the previous owner bought from a camper supply place. They do stay on much better than elastic edged fitted sheets - but I don't use them as 'sheets' - they ARE the covers for my matresses instead of the 70's herculon stuff that was originally on them. These pre-made camper sheets are much rougher fabric than my home bedsheets, and are not as soft to sleep on. But they do make great 'covers' for my mattresses, as they are much more washable than the old upholstery covers.
Instead, we use single or double sleeping bags on the beds. With the sleeping bags, whether tent camping or PUP camping, I have always used sheet liners for them. If you take a two twin sized flat sheets, and sew them together in a long pocket, starting halfway down the long side, across the bottom and halfway up the other long side, you get a liner for two sleeping bags zipped together, perfect for a camper double bed(48"-54" wide. I would imagine that two 'double bed' flat sheets would be a good fit for a queen size mattress with an extra large sleeping bag.
I have found single flat sheets, in whites, colors or prints at WalMart, Sears, etc, on sale, for less than $5.00 each. I have used them in the past to make curtains, sleeping bag liners and all kinds of stuff. you can't buy plain fabric that cheap anywhere else!
I prefer to buy sheets in individuals rather than 'sets' (one fitted, one l flat and pillowcases) because we often use an extra flat sheet on our beds at home on top in summer, or I use all flat sheets on my son's waterbed instead of 'waterbed' sheets. The last set I got at Sears, just a month ago - were 300 thread count cotton!
those will feel really nice on a hot summer night!
1973 Starcraft starmaster 6 - a work in progress - http://home-and-garden.webshots.com/album/558473066XXMupb