If you need the model on the bottom - and you have enough room to spread the upper units all over to get to it - you didn't need the storage units to begin with. ;-)

I use $13 Robart stands and furring strip/PVC pipe w/insulation racking. Cheap and infinately expandable - and any model and wing is readily available.

I also have a few "built-ins" to get models off the floor (nothing worse than backing up and hearing that sickening "crunch" sound).