I had same problem when I added my Snug-Top shell to my 2007 4x4 DCSB. I had/have 4 OEM leaf springs, and the shell consumed all the payload ability. Saggy rear end resulted. I added an Air Lift brand set of rubber airbags to the rear suspension. No drilling, bolt-on kit was about $200 and it worked! Manual-fill via bicycle-type schreader valves which I located at the lower corners of the rear bumper. I fill with a small bicycle hand pump ( bike frame mount style pump). Add a few PSI when carry a big load, discharge when not, or leave it in. You can watch the read end go up and down with each pump.