We have the Fiamma XLA rack fitted to our Hymer, and it is great. As with all German caravans we have a long A frame, about 5 ft from the front of the body to the hitch which gives plenty of room for the rack, gives turning clearance, and incidentally helps with towing stability.
As the centreline of the rack is back about 3 ft from the hitch and as this centreline is say 10 ft from the axle the bikes only add 10/13ths of their weight to the noseweight! Our lightweight mountain bikes weigh about 11kg each, so that is only 22kg x 10/13 = 17kg on the noseweight.
I have noseweight of 90kg with 2 bikes, 2 x 10kg BP gaslights and spare wheel in the front locker.
The only drawback to this arrangement is that I cannot open the front locker properly with the bikes on, I can reach in to turn on gas or get tools etc.
Hope this helps.
Pete