I bought Air Lift bags for both of my Crown Victorias, not for towing, but, because that they are a sedan that was manufactured around their ride. Hauling luggage or anything in their trunks causes the ride level to be affected.
Bump stops are last resort on your suspension system, they don't increase capacity, only keeping it from over stressing the springs.
You could use an add a leaf, it may create a more harsh ride.
I'd bag it, adjustable ride when you need it. DO NOT try air shocks!
2011 Jayco Jayflight 22FB
2004 Ford F-150 5.4 Triton, K&N FIPK, Magna-flow muffler