I tow a 24ft featherlite (a serious trailer) with a 99 M3 track car + track stuff. Max rated weight on the tongue and total weight.
I use an electronic brake controller.
https://www.etrailer.com/bc-2012_BMW_X5.htm
The car struggles (shifts a lot) above 60mph but manages for the short time I'm on the freeway. I get 12-13mpg, visibility sucks without extended mirrors. Dealer installed the BMW approved hitch. 6-7 wide should not be a problem, don't buy a steel trailer.