I just found a good deal on some Hepco Becker Standard Aluminum Cases. Really well built but when I tried to mount it on my 990 with the AdvTank I ran into a major problem, the aux tank was in the way. Very depressing.
See how the cross bar can't go down enough to meet the side rack and the cross bar towards the center mount does not meet the fender.
I did a little research and another advrider inmate had a good suggestion (possibly in this thread), move the tank inwards, a little bit. I moved the rear end of the aux tank in towards the wheel about 5mm (there is still plenty of swing arm clearance and I plan to add a brace to prevent any further flex), then I spaced the rear cross bar up about 5mm from the fender. The path of the rear upper cross member just touches the tank. I added a patch of curly velcro to the tank to take the brunt of any abrasion. Velcro is very abrasion resistant and is cheap to replace. To level out the rear luggage plate I added spacers on top of the grab handles. (adding spacers under the grab handle base changes the spacing too much and does not work, I know this because...)
Drat! I left out a spacer, not done yet.
With the modified HB installation the filler cap is much more accessible than with the Gobi racks.