LCI (Lippert) built the frame and Lippert sells under-chassis tire mounts, storage drawers and a combination of both. You can find what's available here:
http://store.lci1.com/spare-tire-rac...ivers-c76.aspx
Some members with welding skills (or access to a good welder) have installed "crank down pickup truck spare tire carriers" under their RV. That takes some fabricating and at least some experience in welding and metal work. The Lippert components are pretty much "bolt on and go" systems.