Sam,
I have two solar panels on the roof of my Apex 8 for 220 watts total along with a Blue Sky Solar Boost 2000E MPPT controller, a Xantrex ProSine 2000 watt inverter/converter/charger, and two 6-volt Trojan T-145 batteries. I am also pretty loaded in terms of being fully optioned with just about every bell & whistle Outfitter offered for the Apex 8, so my overall dry and loaded weight is no doubt up there even for a pop-up style camper.
For stability considerations, please keep in mind that we first started with an '07 Dodge Power Wagon. I have previously written a lot about that unfortunate event, however, long story short ... it was a major mistake. Even with Firestone Ride-Rite air bags, the stability was so bad (especially on-highway), that just driving on an Interstate with our Apex 8 on board made you feel like your life was passing before you. The ride height was too high for vertical COG considerations, and the off-road tuned (aka "weak") springs were simply not up to the task of adequately supporting the weight of even a pop-up camper.
When we traded in the Power Wagon for the 3500, it was a night and day comparison in terms of substantially increased stability and load carrying capacity. Maybe it's because we started with such an unstable platform to begin with, but the change was so dramatic in the positive direction that I would be hard pressed to complain about it either for on-highway or off-road use. The air bags did get transferred over from the Power Wagon, as well as the 17" forged aluminum wheels with a set of load range E 35x12. 50R17 Toyo Open Country M/T tires. In terms of the wheels, I don't know if it is actually true or not, but I have heard from more than one source that the Power Wagon wheels I have are slightly different from the look-alike 17" aluminum wheels on the 3500, in that the bead area of the rims have an improved bead-retaining design for aired-down tires for off-road use.
Suspension-wise, I didn't do anything before the White Rim Trail trip other than get a set of Rancho RS9000XL shocks, and to install the full array of skid plates that a Power Wagon has. Since the WRT trip in March, I had a Buckstop Baja front bumper and Warn 16. 5ti winch installed, along with a 2. 5" Tuff Country EZ-Ride leveling kit (to help counteract the resultant front-end sag from the 300+ lbs hanging off the front with the new bumper & winch combo). I have also installed a Defiant/RadFlo steering stabilizer, along with a Defiant steering box sector arm support assembly. By the way, I did not need the leveling kit for the 35" Toyo tires ... there was plenty of wheel well clearance as-is.
I am not going to blow the smoke some do by saying that with their Ford F350's, they don't even feel their Apex campers back there. I certainly know my camper is indeed "back there", but I honestly do not feel the need for a rear sway bar. While it would be OK for on-highway use, I do not want a sway bar back there for off-road operations, as it would excessively tie-down the rear suspension IMO (which is pretty stiff already in the 3500, along with the air bags). Perhaps it wouldn't be a big deal if you didn't do too much in the way of more rugged or challenging off-road trails. As it is, I have been looking for a way to disco my front sway bar to get a bit more front end articulation for rougher off-road stuff.
By the way, hanging that 300+ lbs worth of bumper/winch off my front end and gaining a net 1-1/4" increase in front-end ride height did adversely affect my front end handling with more bouncing around and less precise steering. However when I installed the Defiant/Radflo steering stabilizer and steering box sector shaft support kit, that counteracted most of those issues. However, I will still likely go with a set of higher spring rate front coil springs at some point (and ditch the leveling kit spacers).
I am not sure why you are having the stability issues you describe with your rig, especially since our respective set-ups seem to be essentially equivalent. I do agree that going with a set of 18" wheels (instead of 17 " rims) with 35" load range E tires will lessen the side wall height and will therefore stiffen up your ride. Anyway, let me know how your new rear sway bar works out for you.
Good luck,
Don
P. S. We did the Alpine Loop (Engineer Pass and Cinnamon Pass) along with Ophir Pass in the San Juan Mountains in southwestern Colorado last month, which was more challenging than the WRT in many places. I am in the midst of writing that trip report up.