I wouldn't even consider a 7' wide trailer if I was going to try to pull it with a 4 cylinder. A 6' wide is a
big maybe. I'm thinking 5' wide.
Take a look at the trailer in this post:
http://tnttt.com/viewto ... ht=#862612
That trailer is all aluminum - very light weight. It's like pulling a parachute though. I tried to pull it (completely empty) one time with a 1991 Toyota 4 cylinder pickup. 4 cylinder, 5 speed. On the floor in 4th trying to pull it. Never tried that again. The Passport in the picture had a V6. It would pull it OK loaded - but
just OK. Not real well. The motor box on that trailer is 6' wide.
I have a 6 X 10 that my son pulled home from where I bought it with his 4.8 liter Chevy V8 pickup. He only got ~ 12mpg...
Pulling an enclosed trailer with a pickup is like pulling a parachute. I've talked to several friends that pull(ed) their trailers with vans or pickups with a camper shell and they have all said that a van or pickup with a camper makes a difference. Cuts down on drag.