Bill touts one of the best ideas, but the FMC Magazine's January issue I believe is more thorough if not more reliable; Motorhome's guide didn't include the Ford Edge, for example, and FMC Magazine did. Motorhome also has a lot of ads you have to put up with. As an FMCA member you may already have a copy of theirs, but if you want another "viewpoint" you can see Motorhome's online as a PDF here:
http://www.motorhome.com/download-dinghy-guides/ A few years back I had a question about some vehicle's report I read in FMC Magazine and exchanged a few emails with their editor(s). I was exceedingly impressed with the thoroughness of their answers, their genuine concern, and the extent of research they had to have gone into just for me. They had a team of automotive authorities dedicated just to the guide, although Motorhome may also. As I recall it did result in a slight modification in the report configurations of future FMC guides.
Keep in mind always that they can only report what they are given by the vehicle manufacturers. Manufacturers regularly change their minds, and what may be true in January may not be so in February. About 10 years ago, Honda (and Toyota I think) went through a spell of approving cars for towing, having bigtime warranty issues with trannys, etc., and then withdrawing approval. What engineers think will work towed 4 down in a new drivetrain invention, may not in fact work in the real world. Thus it is a real advantage to have venues like this Forum where you can know how existing owners have fared with a particular vehicle, including older models if you're buying used.
I can say that FMC editors go the extra mile to confirm what they eventually print, and have only their members' interests at heart. Nevertheless, always firm up with a vehicle's owners manual and with the manufacturer itself that it is towable 4 down before putting it behind your coach.
Joel
