When I looked "utility" "cargo" "car hauler" have basically the same GVWR for comparable sizes. My 7x14 cargo has 7,000lb GVWR, once you get to 16 or 18 ft you can easily get a 10,000 GVWR and it goes up from their.
I'm sure the OP knows about weights but many folks forget the 7k gvwr trailer doesn't have a 7000 lb of CCC.
Example one of my flatbed car haulers has a 10000 lb gvwr but weighs 2640 lbs leaving around 7k lbs of CCC....steel frame trailers of course.
The 18' 7k car hauler I had weighed 1520 lbs.
I'm sure a cargo trailer frames are about the same construction.
My neighbor lady has a 22' cargo she does house keeping and yard work (retired OTR driver). Her trailer sat really low to the ground making it drag getting around on new yard work sites and carrying a 4wd 26 hp tractor. One of our neighbors is a certified pressure welder flipped her trailers axles and added 5/16" side plates to the spring hangers.
Maybe I missed it OP but are you planning more roof/walls/floor insulation ??