need opinions on air bag rear suspension idea.

[LittleHoe]

Ok suspension pros... I need some opinions on an idea I have... I am thinking of removing the rear springs from the shocks and installing some custom mounting plates on the bottom of the car and on the rear axle as far to the outside as possible and then mounting a suspension air bag on either side, that should allow me to lift and lower the rear end as I need. Right now I have fms springs with spacers to try to tighten up the rear end because of the extra weight from the custom fake floor and sub/battery box.

[Dragonhealer]

OK Little,
Looks like I should help out here.
As you have a special situation, the idea is in the right direction
but wrong implementation.
PLEASE don't remove your springs, a stand-alone air suspension
is like tuning a formula 1.
I know you can get a full system for full sized trucks (big bucks)
but this is totally wrong for a Festiva!
Well within the scope of the average mechanic are 2 good
solutions. (1)air bag supplemented shocks, these will have to
be custom jobs. or (2) separate air bags mounted on perches
added to the rear beam bearing on plates installed under the floor.
Either of these supplemental systems can just be plumbed
together with a schrader valve installed in a convenient location,
like the fuel filler plinth, and add enough air to offset the added
weight.
This used to be a common solution for a station wagon tow package
through the 80's, and in your situation may be appropriate