Back to help. See you had a Work & Play. Mine was 8' wide, and while I liked the interior space, your idea of a 7' wide trailer would be better in many ways.
I towed with my half ton Avalanche with SnugTop topper, and up hill from Ft. Worth to Amarillo, to Moab, in head winds I was getting sometimes less than 7mpg per tank. With a tail wind, up hill, east bound out of Albq. NM I was amazed to get a 12mpg tank. It seemed to be the wind, more than the weight of the trailer with a GSA and X-Challenge inside. I once towed 400 miles to the coast and back without bikes, and got hammered on mileage again with winds.
8' trailers required mirror extensions to be able to see down the side of the trailer on the highway, and backing. The truck is 6' wide, standard mirrors work well with 7' trailers.
If doing again, I would sure buy another Work & Play, but if I were building, v-nose, 7'. I would also go tandem axle, hoping to be able to tow on a flat tire till I found a safe spot to change the flat one. And with a tandem you can often drive up on a stack of wood blocks with the single good tire to change a bad one, without risking a jack accident, or messing on a badly sloping shoulder.
Pantego (DFW) TX
1998 Foretravel 36' Unicoach 295
Without a bike for the first time in 15 years. And cancer sucks.