Where can I find sheets that fit?

I found a couple places that make custom sizes but they are expensive.

I ended up just going with a (full size) sheet set and mattress protector. I had a set on the guest bed so I checked how it fit. It was a little tight but you can't tell. I also went with the full set instead of trying to look for or spend a fortune on a custom one because I also had a spare memory foam mattress topper that wasn't being used I threw in the camper. It's also still easy to lift up either side to get to stuff underneath.

In my 5 wide, I have my mattresses on top of two REI Camp Bed 3.5 inflatable sleeping pads. Its a perfect fit inside the cabin. Using two pads allows my wife and I to control the firmness individually. I use full size sheets and they fit fairly well. I also use bed sheet elastic holder straps (Amazon) to help hold the corners of the fitted sheet in place.

Sheet straps really work..we have the XL and use twin fitted sheets...