Before I bought my TJ I had a P/U. When I bought my TJ I missed my P/U so I bought a 5X10 cargo only a few months after I got my TJ, that was back in 01. I have used that trailer so many times I can't begin to remember them all. I have had friends and family members use the trailer countless times.
I have had it loaded with other 3k worth of crap and towed it cross country, I wouldn't recomned anybody doing that.
I also have a covered 6X12 that I tow behind my TJ as well as a 14 foot Jon boat and occasionally an 8X16 foot (never very loaded). AS long as you don't overload your trailer I would say up to a 6 x 12 is easily a safe bet.
01 TJ, 34 Super Swaper TSL 34x10.5 bias, Winch, locked, belly up, some armor.