Sorry if I mislead you, but I do not have air bags. Was just saying that the ultimate set up would be a truck w/ just 2 airbags like semis have.
I want to say that carringb may have hit the nail on the head. Although I haven't weighed this truck/RV combo yet, last year the RV pin was 3700 lbs (same RV, diff truck then). I had the upper and lower Stabil-Loads and ended up removing the uppers and just going w/ the lowers and had very good results. Using both was a BUCKBOARD ride. If I read carringb's post right, should I install the uppers so the aux spring is engaged all the time? Won't that make for a harsh ride unloaded? If I do re-install the uppers, not sure how well they will work so to speak as I cut them down substantially on last truck so they weren't hitting all the time unloaded. OR on the other hand, they may "take up" enough of the gap to lesson the "bang" upon rebound?
In regards the Ford having too soft of springs, I'd agree w/ that on their 250's, but their 350's seem pretty snug.