The little elastic straps that look like "idiot mitten clips" are available at Walmart, in the organizational section - closet systems, coat hangers, etc. I just got some today, to replace the safety pins I've been using to keep all the components of my bed in alignment-can't find sheets small enough for my 28" mattress. I like sheets with 400 or higher thread count, too, which aren't even available in a smaller than full size - guess they think if you sleep in a single bed, you're a kid! So I wrap the flat sheet around the foam mattress & memory foam topper, then pin it tight. I think that springing for good fabrics on the bed makes me happier about being on the road. lol.
The extra safety pins are stuck in the headliner, above the driver's seat - handy, especially if I ever need an impromptu weapon!