I have been pulling my motorcycles in enclosed trailers for more than twenty years and more than 50,000 miles. Our current trailer is a 6.5' x 12' Wells Cargo, dual axel model. I carry a 900 pound motorcycle (Gold Wing) 100 pounds of tools, motorcycle clothing, spare tire, bottle jack, and often boxes and buckets of rocks, squash, wood, and other heavy stuff. I don't feel the trailer, except that it affects the braking a bit. (The trailer has brakes.)
I haven't found any decrease in fuel mileage when pulling the trailer. However, I use the weight of the trailer to my advantage when driving in hilly conditions and let the rig increase in speed going down hill and then allow it to slow going up hill. I seldom use cruise control.
Backing with the trailer is not a problem because the mirrors work well and the RV doesn't turn as sharp as a pickup truck so the trailer is easier to manage. Just back very slowly and watch the front end when backing and turning.