We have a 12x6' vee nose enclosed trailer (14' to the front of the vee). The frame is aluminium and it is nice and light, and tows well. I think it is actually a motorcycle trailer. The racecar just squeezes in as it has barn doors on the back, if the 10x6" wheels had more offset, it would be touch and go, we have 3" group 2 flares. We have to push it in, because there is no way you would get out of the car once it is in...

We learned the hard way that trailer tires become exponentially stressed for every 5mph over 55mph.Had a blowout in the middle of the night in the middle of nowhere in Utah. Took the fender with it...

Next trailer will be a bit bigger to accompany bigger racecars and will definitely be tandem axel.

That said, we have towed thousands of miles with it and except for the blowout, it has been great.

If you get a 102 by 28 there is room for a pickup and a wildgoose camper with room to spare for luggage and spare parts you do not want your wife to know you bought.
You can name it "The Queen Mary"

I was going to look at a 7 x 14 tandem this weekend but it sold last night.  Thanks for all the advice.  I will watch out for the roof issues.

I use a 6 x 12 with a side door but it is difficult to drive a Mini in at that size. A 7 x 14 would be a better bet for room to get in and out, not sure how Jimfai is doing it with a 10 foot trailer as a Mini is longer than that unless he is using the front area in a V nose.
The trailer with the least amount of rivets on the outside is the best one to buy but most are cheaply made and down the line suffer roof leaks, for that reason try to get a one piece roof. Also i have found the ones with the rounded corners on the roof instead of flat roofs tend to have less leaks. A V nose is good for the extra room to tie down and less wind resistance. A double axle is usually preferred but not mandatory.

i have a couple of the 6x10 enclosed ones from home depot with the ramp back door and a side door.  a mini (without sportpack flares) will fit in there just fine as will an mg midget, i used mine to transport both types of cars.   i just drilled holes and attached large eye hooks at each corner of the floor.  you would be hard pressed to get to the front ones if you get a trailer without the side door.  

What size enclosed trailer would you guys recommend for hauling a Mini?  I would like something somewhat compact but still safe to haul a Mini.  Is there a particular brand or anything to look for?  

Thanks!