Hit the local autoparts, most have helper springs that either attach under your existing springpack, and extend front and rear, or the type that attach under the springs, either (or both) in front or behind the axle. I put 2 sets, one in front 1 behind on an old dodge 150 I had years ago. Much stiffer ride unloaded (doesn't sound like an issue for you) and far less squatting loaded. This won't do squat for breaking, or the load on your axle, tires, etc.
I was able to put them on in the garage with a floor jack and a ratchet. Assuming you have a jack for changing the tires, and a socket set you should be able to do it in the parking lot.
