Something you might find useful, from the junkyards. The 4Runner rear suspension, back in '96-'97 was prone to hitting the axle bump stops when heavy loads were put in the back (or too much tongue weight on a trailer....like we'd EVER do that, right?!). Anyway, to make a long story short, there was a service bulletin that allowed fitting different rear coil springs and bump stops based on customer need.
Those '99 and newer rear axle bump stops are urethane and progressive action. You will find the same progressize, urethane bump stops (but in different lenghts and diameters) under the back end of various vans. Same problem, so to speak, of too much variation in load usage by the customers.
Some of the off-road guys have learned they can "adjust" the urethane by how much they cut off (it is tapered and stage-stepped in various applications). This lets them get a quicker take-up of the load, at end of travel. Pretty cool stuff, and not "rebound springy" like rubber can be.
JimL
PS: Time to mention the engine/transaxle shock absorber on front-wheel drive vehicles. They have this neat little, short, booted shock absorber with zero-zero valving. It is made to handle very heavy unsprung mass, to keep the powertrain from jumping up and down under the hood (on segmented concrete highways and such). You will find them bolted between the bell housing and frame, toward the front center of the engine bay.
The upper cushions can be adjusted for clamp tension with the double locking upper nut, which lets you adjust how much movement to allow before your shock takes over. Heres a pic of one from a Camry, as I used on a street rod front axle.