For my tent mockup photos, as I said I had the tent setting on some 2-by wood lying across the top edge of the tub, but the tent could easily be mounted on the trailer even without the fiberglass hard cover (or a DIY-built wooden cover), by attaching rack bars to the tub:
Thule rack bars on tall stanchions can be mounted to "fake rain gutter" plates bolted to the sides of the tub. Then the snap-on tonneau cover goes underneath for weatherproof protection and easy access for the cargo inside the trailer.
The rack bar approach is a good one if you plan to use the trailer for multiple purposes - remove the tent from the rack bars and you could put your kayaks on the rack bars, or bring plywood home from the lumberyard on them. Remove the rack bars and you've got full access to the bed for tall cargo.
Or the tent could be mounted on the fiberglass hard cover I've got planned...
Or an easy-to-build DIY plywood cover: