Bertc, We have a similar rig, 2010 LTV Free Spirit with rear sofa/bed. After using a combination of old sleeping bags, then a home-sewn sleeping bag with 2-way zipper, I upgraded and ordered a queen RV Superbag with cotton sheets that velcro in. And I wish I'd invested in that 3 years earlier. I called to inquire about rolled-up size for storage, and the owner answered the phone. He advised sizing by sleepers size in addition to bed size. (combined weight > 350 lb, get kingsize.) We got a queen and it's just right.
RVSuperbag.com