We located a trashed 25', 2 axle travel trailer...stripped the box and sold the appliances...rebuilt the hubs and electric brakes - viola' cargo trailer/car carrier frame.
The trailer's GVWR does not change, but with a much lower UVW, the cargo weight allowance becomes very high.
Went to the DMV to get a SPCN (special construction) title which is cheaper than keeping a TT title in our state.
Fabrication was a deck of affordable of 2x10's three wide for each tire track (avoid having the ends in-line) drilled and bolted with plates to the frame with carriage bolts for a smooth surface (don't drill the metal frame to maintain any strength).
The lumber and steel frame together made the trailer very strong.
You could cover the whole trailer frame with decking for a flat bed.
You could build folding ramps on the end.
You can add Railing around the deck edge which will make the trailer even stronger.
We now have a toy hauler, so when we needed, we sold it for more than the total cost to build it.
Another option if you want to just buy something...a "Tandem Dolly" gives you a tow dolly like you use now -plus- a deck added on the front for the bike and BBQ/Kegger...like:
Landgrebe is kinda' premium priced, so you might shop around for price point options.