Shimming the rears won't change the rear weight bias that has your front end geometry out of whack. Neither will the addition of air shocks. I think you might load your tank full or load it as you most often drive it, then take it in for a front end alignment. If the alignment is done with the VO tanks empty or nearly so, it won't compensate for the light front end when the tanks are loaded. You have the weight hung out behind the rear wheels, I would guess; that must make handling at highway speeds interesting.
It may be the extra weight is causing the car to "push" more than usual which might wear the outside of the front tires as you describe.
I wouldn't think 225 pounds of extra weight would cause such a dramatic problem as you describe. What does the second tank weigh? How about the heating devices and that lot? Did this problem start only after you installed the extra tank and mechanisms?
I have a 21-gal aluminum tank with aluminum supply and returns, both of which are within rubber heater hose and heated by the coolant. There is an alum. coil within the tank. Not sure of tank weight, but it's as light as they go. photos of tank and lines
The heater section is up front under hood. photos
It's not much weight, but it's up front.
Yes, handling is "interesting" and takes some training. The rear end flops around like the fattest bootay you've ever seen in the hood, so to speak. I feel like I am slalom skiing. It's a similar motion on my body. Going into a set of curves, I swing the wheel and move to the motion with it, back and forth, with the rear trailing behind rather than keeping pace with the rest.
Please explain what happens if I align the car with the tanks full. Is it possible to do so? I am thinking the max adjustments will not account for such weight.
And why won't shimming work? If I raise the rear end up to account for the weight, won't the front wheels be brought back in correct toe? See the worn tire photo below.