sbergherr, If given the choice, a 5er "only". If you do go 40 ft., you will only increase your overall length by approx. 2 feet. You will have much greater living area as well as greatly increased storage ( at least over most TT's). I believe that you will find that the 5er is more comfortable to tow, and likely more stable on undulating highways. Also, when backing or on a sharp turn....you can virtually go to 90degrees. Though with a short box you are somewhat limited on the 90 degrees, but still greater than the TT.£There are more 5ers that offer 4 season capabilities....though with many it is a sales ploy! Also, when purchasing your hitch, make certain you get the 4 - way articulating head. You will appreciate it, unless you always camp on a nearly perfectly level site.