Sagging Rear End

My RRC suffers from a little rear end sag. That is, the back sits a little lower than it should, even when stationary. The self-levelling unit has been blamed as the culprit, and I even have a spare unit that I could fit. However, I'm thinking long term and as these are no longer available new, I feel that at some point in the future I am going to have to abandon the self-levelling approach and go down the route of fitting stiffer springs to the back end. I have seen 'police spec' RRC springs advertised and these seem like a good solution for the ride height as they are slightly longer than the standard items. Matt Savage also advertise air bag assisters that sit inside the coil springs and can be inflated when carrying heavy loads. Can anyone offer some advice?

I run HD springs on one of my RRCs. Sits 1 1/2 inch (approx) higher than standard. Not much different when loaded. Same length as standard springs but a lot thicker so less sinking.

I can strongly recommend the airbags, they're easy to fit with no downside.

On sagging rear end, check your rear cross member. On my first RRC I thought I had a sagging rear end, fitted HD springs to find it riding exactly the same. Suspected the Boge unit but the air assist springs were cheaper so went that way. While fitting the air springs I got the chassis exactly level but the rear still looked low. It was then I noticed the rear cross member was completely shot and my 'sagging' rear end was in fact that the body had dropped down onto the chassis at the back. If finished up where the rear tailgate was down on the bumper!!