I wouldn't worry about the gears, the Auto will change down if it needs, not like you will have much weight behind you anyway.
Admittedly i have a turbo diesel Land rover for towing, but with a round nose on a 7x5 trailer(with extended drawbar and drop front and rear tailgates) I can barley feel the trailer behind me, and the trailer is 365kg's empty so you do the math.
Ive had two minis on a looooooong car trailer before and was also not too much of an issue, 6th gear on slight inclines, drop it back to 5th if the hill looked like it would get a little nasty just to keep the EGT's down

just make sure you strap the car town well so its not moving everywhere, a shifting load is a pain in the bum!
(don't take the photo of my roundie badly strapped in on my trailer in one of my threads as a guide though

was a 4km trip and I was feeling lazy!)
Leroy.
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1967 Mini Deluxe bucket of rust and mismatched parts powered by a 1360cc and a destroyed gearbox missing second gear
