Any of the current Ford hybrid and plug-in hybrids can be towed four down (C-Max Hybrid, C-Max Energi, Fusion Hybrid, Fusion Energi, Lincoln Mkz Hybrid).
As a bonus the Energi models can go 20-25 miles on electricity alone (you can charge them up using the campground plugs--I use the 50A plug to charge my C-Max all the time).