The Navigators already have the air suspension on the rear. They also have independent rear suspension (same as Expedition). I've never towed with either but I have towed with a 1/2 ton (with rear coils) Suburban. The 1/2 ton suv's are designed more as people movers and to deliver a comfortable ride. Like was said earlier though, they can be upgraded to haul heavier loads. The payload capacity of any vehicle is based on the sum of its parts. Single rear wheel trucks for instance are limited by the rear tires more so than their frame, axles, suspension etc as compared to their dual rear wheel counterpart. Where SUV's are at a disadvantage compared to a pick up is that they're shorter and heavier right off the bat. If you where to try this I would recommend a higher end weight distributing hitch/sway control and brake controller. Also pay attention that your truck is equipped with an external transmission cooler and an accurate temp gauge. If it is not I would highly recommend that you add one. Also, keep in mind, if the trailer starts to sway on you, just tap the trailer brakes (not the truck brakes) to straighten it back out.
