I've been very happy with the Viair 400P, which is popular with off roaders for good reason. I got the automatic version and I'm glad I did. Was like $220 new on an ebay competitor site. I thought about mounting it underneath but it's too dirty down there, so I usually just pack it. It's very easy to setup; 1-2 minutes tops, and always clean as a whistle inside it's carry case. I rigged up a fused always hot connection to CCP2 that sits right there by the open driver's door. I use it often. More about that here
But so far I don't have air bag plans, or really need compressed air for anything. The factory rake plus the VC lift kit (no bilsteins up front) have made it so that even with most of my big ticket heavy items installed the rear is still
higher than the front, so rear airbags would only make it worse (that annoying ~80mph drone sound is gone though). I typically park with the front facing uphill to help overcome this. When on level ground or if I can't face uphill, I can press just the head lift button on my adjustable bed remote for a second. But that only buys about 1-2" before it starts to feel awkward at the hip/chest area while sleeping, and I have to remember to do it every night. A little side to side tilt isn't a huge deal because the bed faces front to back, but I guess it would be nice to be perfectly level on that axis. I just can't tell if air bags and all the gear to make them work are worth the effort. Here's a shot of the adjustable before I put the mattress on. I friggin love this thing. Have used one at home for decades.
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For people with side to side beds, I could see air bags being more useful, but again, with a VC lift and no Bilstein's, you might have a rake even after your build is complete, so airing up either rear bag would make it worse, which might cause you to roll out of your bed, or be at a diagonal. You can build your bed platform to lean towards the back, but it would need to over-lean beyond level and then you'd need to air up both bags by some amount every time, otherwise just using one bag would again create a diagonal or forward lean/roll.
I've read a few people on the forum say they won't drive with the bags inflated anymore. Not sure what that's all about, but might be worth looking into.
Anyhow with the 400P Automatic I have no problems airing down and back up without interruption even on hot days. The automatic stops itself between tire fills, and I usually only drop 5-10 PSI even for thick sand and gnarly death valley jeep trails and just skip filling back up on the way out. If you air down too far, you start giving up ground clearance, which is a bigger issue on most of the rough roads I take, even with 265/75/16's.
The factory PSI ratings on the van are also very high because they have to cover even heavily loaded rigs, and while my build has a massive power system, it's still not heavy enough that 5 PSI matters, yet that's usually all it takes to trim the edge off of the ride harshness and improve traction a bit. I've been through insanely thick sand like that without any issues. Just gotta keep a bit of momentum. You can go much slower if you really air down but then you definitely need to stop and fill up on the way out, and again, you lose some ground clearance.
I find I'm usually not in the mood to pull over to refill after I get off the jeep trail and back onto the nearest highway...something about craving a burger, or just looking forward to getting to my next stop. Hard to say why exactly, but my brother is the same way. When it's time to go, it's time to go.