I wish the Mods here would make this a Sticky.
I get asked this question all the time on forums and Facebook pages, and at the local car meets, especially by new wagon owners and folks that take a ride in my car or see me towing boats or motorcycles on my trailer.
The FIRST thing I do on my whale wagons is replace the rear springs with variable-rate Moogs and all four shocks with KYB Gas-A-Justs. The rear springs and four shocks can be sourced from Rock Auto for cheap. Then just tuck the air lines up out of the way in the back, pull the compressor fuse, and BE DONE.
My 96 Roady Wagon has had this setup since 2008, and I also did this on my '92 Custom Cruiser wagon. One of my favorite cheap, easy (other than the upper bolts on the rear shocks), and BEST mods. I'm about to do the same thing to the 78 Electra Wagon project.
Rides great with the MOOGs and the KYBs, still tows a boat fine, handles a full load of people an cargo, and I never again have to worry about shock or hose leaks, ride level sensors or compressor failures. All these components are just too old now...either worn out on the high-mile cars or dried-out on the low-mile cars. It's NOT worth the effort!
Rock Auto Parts and Pricing -
MOOG Variable-Rate rear coil springs, Part # CC623 - $48.79 pair
KYB Gas-A-Just Rear Shocks, Part # KG5504 - $29.89 x 2
KYB Gas-A-Just Front Shocks, Part # KG4515 - $33.79 x 2
DONE....forever.
-Texas Mike
****OH and Bilstein shocks are GREAT if you can afford them and want a bit firmer ride. Likewise many folks swear by the Monroe Severe Service Shocks (Taxi/Police), which are not expensive, but I ran those a year on my 96 Roady Wagon and found them just too harsh over bumps, potholes and highway expansion joints.
OH I also tried coil-over rear shocks from Autozone for a time, with the stock rear springs, but the actual shock inside the coil is really tiny, so the rear end was "bouncy". Replacing the actual factory springs with the Moogs and installing the KYB shocks was a MUCH better way to go.
The KYB Gas-A-Just, to me, are a great balance, they really firm the car up but it still rides smooth over all road conditions, and as you see above the pricing is very fair on them.
Hope this helps folks!