I have a 6.5' x 12'
Rance Rough Rider aluminum single axle (3500#) trailer that I haul either the Talon 1000R2 FLV or the Pioneer 1000-5 on. The nice thing about that trailer is that it only weighs 660# but has a GWVR of 2,990#. That means nearly 2,300# of payload capacity.
That said, if I had it to do all over again and wanted an open trailer, I would still by a Rance aluminum trailer, but:
1. I would get a tandem axle trailer. They offer the same trailer with tandem axles (GWVR 7,000#) in 14, 16, 18, or 20 foot lengths. These weigh from 1,125# to 1,475# respectively, which means payload capacites between 5,775# to 5,525#, respectively.
2. I would get a longer trailer. Sure, the 12' SA gives me plenty of room for the Talon or Pioneer, but it would be nice to have more room for strapping some gear down on the trailer (and not in the truck bed) or maybe even getting a second buggy on there (not sure if the Talon and the P1K5 would fit on the 7'x20' together).
I installed e-Track on it and use Erickson tire baskets, so I went with the 5/4" x 6" treated wood deck over the aluminum deck.
Best of luck in your search.