I'd first contact a UK member of the board and have them give you the max towing limits in their owner's manual. I haven't seen towing limits listed in the US versions for decades.
The two limiting factors will be:
#1 The tounge weight. Most BMW cars are limited to 75kg (165 lbs). Weight the tounge of your trailer to make sure you will be under that. If it's over by much at all I'd just forget it.
#2 The max UNBRAKED towing limits of the F30 will not be close to 3,000 lbs. It will probably be in the high 1,000 lbs range (maybe 1,600 -1,800 lbs.). But, the BRAKED trailer limits will probably be in the 3,500 lb range. Even my 138 HP/ 138 FT-LBS E36 318ti has an BRAKED towing limit of 3,306 lbs. You will need to add trailer brakes if you want to meet this limit.
And for the hitch itself, the US made ones (u-haul, Curt, etc..) are mostly class I, as you've probably seen. You might need to order a real Euro hitch (Westfalia, Witter, Bosal, Thule, etc.) to get the max towing capability. Check their websites for limitations on their hitches. For example, Westfalia has F30 hitches in their online catalog but they don't list max weights, yet. But, their E90 hitches in both fixed and detachable versions have max limits of 165 lbs tounge (75 kg) and 4,000 lbs trailer (1,800 kg). That will do the trick.
You can buy euro hitches at
http://www.pfjones.co.uk. They will ship to the US for about $220.
I've towed with my 318ti for many years and find it very useful
Here's my 5x8 Aluma that puts any SUV to shame. When things are too big for the family Suburban, we use this (and get better fuel mileage than the Subruban could get) Good Luck!
