I have seen double deckers, not sure who's making them. So far with 2 boats I end up putting the second boat with frame attached on top of my fully rigged boat, then most of it's gear goes in the bed of my truck.
Ya, it would have to be a pretty wide trailer, I had to build the deck over the wheal wells on mine, leaves some space for shorter items under the raft, such as the spare tire, jack, garden hose for the eco safe. Kind of a compromise, still better then full d-rig and rolling boat though!
" I wish I were a headlight, on a North bound train..."