After being tutored by an old friend who does a lot of sewing, I ended up keeping the Elna Lotus sewing machine. The first project was to take a flat percale cotton king sheet (purchased at Walmart), fold it in half sandwiching 100% cotton quilt batti, and sewing it together (trimmed to the exact shape of the mattress). The pad was pinned and quilted every 4 inches. Elastic was sewn as loops on the corners - voila!
Then I took good quality queen fitted sheets (again from Walmart - some were percale cotton, and I did also use the cotton-poly ones too) and resized them to fit, including the curved corner. I also bought the elastic attachment for the sewing machine and sewed 3/8-inch elastic around the bottom so it would hold the fitted sheets in place.
While there is some roughness in what I did, it fits well and holds its fit. I made the last pair of fitted sheets while I was camped (actually hosting) at Mystic Springs in Pensacola. The place was very quiet so I took two of the long tables in the clubhouse and put them together to layout and sew the sheets.
In order to lay out the sheets, I did make two templates using cardboard: one was for the curved corner; and the second one was for the 4 darts making up the round corner.
All-in-all, it was well worth the effort to learn to do this, and the results are very acceptable.
1987 Excella 32-foot
1999 Dodge Ram 2500HD Diesel