Have a 1931 slant windshield model A have a chance to pick up a 7by14 enclosed trailer good choice or not?
A covered trailer is nice, assuming you get it big enough, because you can also use it to store your A when you are not using it. I have an open trailer and kind of wish I had put in a little more money into it and purchased a covered trailer. Being I do not have a covered trailer, I don't know if this is true but I would assume you would need more power to pull a covered trailer because of the weight, wind catch, etc. But am not sure of that so others on the Barn can give you ideas about that. If you have a big rig, they you have no problem either way.
Build that work bench! I have a '99 20' X 8½' Haulmark for my coupe and it suits my needs perfectly. I built a work bench in the front with tool and spare parts storage underneath, a drill press, 6" vise and grinder/wire wheel. I wired in a connection and receptacles for 120 volt power. There's plenty of room to get in and out of the car and its plenty long enough for my steele trunk lengthwise. I pull the rig with a '99 Tahoe with a 350 (210K miles) and get 9.5 MPG (17-19 without the trailer). The trailer serves as a garage and workshop. I have used it at a couple of "away" events and it gives safe, reasonably secure, dry storage for the car at night yet I have a portable workshop with tools, parts and supplies readily available. I couldn't have a smaller trailer for what I use mine for.I think that will be REALLY tight. Mine is a 8.5x20 and I just have enough to get my skinny butt out the door.
Length you don't need anywhere near 20', but I wanted a workbench up front. I just have not done it yet.