I had a big response typed, but for some reason it did not post :(
Thanks for all the advice and tips everyone. Feeling a bit reassured and getting more comfortable with the big truck and load! I took the unit for a 1/2 loaded test drive Saturday night and it handled pretty well actually! I even took it on some off-kilter roads and everything handled nice. I also built a 2" 30 psi foam/rubber mat combo to sit under the camper for cab clearance, that may be helping slightly too. The Happijac Turnbuckles make a nice difference too. I live in a very windy area, so sway is my primary concern, will have to test again when it is windy out, but was happy with things this time around. The truck will indeed primarily be used as a camper unit, so not too worried about unloaded driving. It is also equipped with (I'm assuming) a stock sway bar.
Seems like the consensus is a leaf spring of leaf spring engagement upgrade and perhaps a sway bar. I don't really want to go with 19.5s, already have concerns with clearance and don't want to add to that. Would consider a wider tire though as next upgrade.
Any tips on setting air bags in the meantime? I had them pressured up so the leaf springs were just engaged while loaded and things road nice, including over large bumps. May have been over utilizing though? The truck sits okay without them pressured up, the camper itself has a bit of a lean though. All the pictures I've seen with the 30C10.11 seem to have the lean, must be a design thing..
As far as tires go, a 245-70-19.5 is literally the same diam as what you have, 33.2" 9.6" wide vs 10.8 for current one. BUT, capacity is 4100 for an F rated tire at 90 PSI, n H rated tire at 120 lbs is 4900 per tire. I'm not seeing a spec for G rated, at 110 psi, around 4500 or so.
Next size bigger is a 265-70, add 200-400 lbs per tire with the same load ratings. About an inch in diam, 10.4" or there about wide. I did not look up these specs either. IIRC the widest 19.5 is a 285-70. 225, 245 and 265 are common sizes. 285s are not as common. 225's are what most of the correct 45/55 series truck have on GM, Ford and Dodge. A few may have the 245 sizes.
Reality, the 19.5 treads are not an issue from a rubbing standpoint etc. If anything, less of an issue than what you have.
Not sure how much your tires can carry, Based on my 285-65-18, probably in the 3600-4000 per tire relm. You could add 2000 lbs per axle with the H rated 245 tires.
