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..
I wouldn't worry to much about going to 19.5's if you decide to, I have factory 20" wheels on mine and combined with the tire size they are 34.9" tall. as for adjusting the air bag, you want to have it so it just keeps some pressure on your factory overload spring, and yes that is a factory sway bar. the helliwig is much thicker but you should be fine with the factory one.
one thing you should do is load it up how you would go camping, even a full fresh water tank. drive to a scale and get your front and rear axel weights. that will give you a better idea about how much weight you have to compensate for and if you only a few hundred lbs over you might just want to keep the airbags and if you more then you know how much spring weight you have to add. raising the overload spring weight and changing that will be much cheaper than playing with the main spring pack, plus it will not raise the hight of your truck. if you put heavier main springs in you could have a 2 or 3" raise on your bed hight which could affect leveling, the stairs and so on.
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.
