The parking dolly was one that I got at Princess Auto (Canada's equivilant to Harbour Freight) a few years ago, haven't seen them again since. It wasn't terribly expensive, around $100 if I recall correctly. It works quite well allowing us to get the bike tucked in the space much easier than trying to manhandle it in. The ST is the low suspension version with no center stand, so the typical Park-n-move type dollys wouldn't work.
Here is a picture of it from their site archives.
The shelf is lag screwed into the 2x6 studs as is the brace. The base framework is 2x4s with a 3/4" plywood top and vinyl tiles. There is a 2x6 doubled onto the base frame overlapping the plywood and tile to cover the edges. Its all put together with construction screws and is quite solid. Plus, the Bonneville is not a terribly heavy bike.
The door insulation is Reflectix, which is basically high tech mylar bubble wrap, and under that is 1" styrofoam panels. The styrofoam is glued on and the Reflectix is held on with sheetmetl scres with washers. the sheets are 4' wide and the seams are taped with aluminum foil tape.