Many of us TC types have gone through the suspension ballet to try to contain the load…a load which is typically just beyond the factory rated load for the truck. With your perimeters, I think a good, thick anti-sway bar is the ticket with the 990, if you are happy with the loaded suspension characteristic as is, especially if it has stuff on the roof like air conditioning. If you are doing days worth of bumpy, off camber trail driving, just disconnect one side of the anti-sway bar and zip tie it up to the bar; and drop the tire pressure down to 32-35 pounds. This suspension freeing move and pressure drop is from the hard core jeep days and allows your tires to be part of the suspension. Great on miles of washboard.
But let’s find out actually what the anti-sway bar does. It tries to keep the axle parallel to the frame of the truck by resisting any off camberness on a graduated scale. That’s why any car or truck with anti-sway bars actually have lots of jerking sway when obliquely hitting a dip, driveway, or hole. It’s trying like mad to keep the axle parallel. On pavement and in curves are where it shines with any top heavy or just heavy load.
Another, more complicated procedure is to find a used set of upper overload leaf springs to add to your rig. The holes in the frame are there. I took this to ridiculous heights by adding one 2000 pound overload spring in the main pack and 3 upper secondary (overload) leaf springs up top and Stable Loads to have 8 leaves per side on the rear axle. The 3 only come into play with at least 2500 pounds in the bed. I cannot recommend air bags of any sort unless it is a factory installed air-ride suspension with a lot of dampening. I have not heard great things about air-ride suspensions and heavy truck campers. Why don’t I like the bags and coil springs for an off road TC? In a word: recoil.
They exacerbate the pitching, sway, and opposing reaction. Dumb old leaf springs simply take the hit with a whimper and say, “Duh, what happened?” There is a lot of friction with leaf springs which helps mollify the rough roads. Dialing in your rig’s suspension can be a painstaking and lengthy process with lots of variables. You want the suspension to take the load and keep the sway down, but be supple and smooth when you have nothing in the bed. That’s a very narrow breach.
To see the end result of many years of experimenting with my suspension, watch this short vid going up the ‘Diablo Drop Off’, a sand hill in Anza in a 10K pound truck camper with 6000 pounds on the rear axle. Tire pressure 20 pounds, the lowest i’ll go on blow sand. After watching this vid, i saw the need for another set of adjustable shocks on the rear axle.
2020 Ford F-350 XLT FX4 4WD SRW SB SC 7.3L Godzilla Gas TorqShift 10R140 397 amps dual Alt dual batts Frnt Dana 60; Rr Dana M275 E-locker 4.30's 4580/4320/4066# payload 7243# curb wt. 11,300# GVWR 5-er prepped. 2020 Northstar Laredo SC, 12v compressor fridge, cassette, 320w Solar sub zero insulation.