The general idea is that your stock suspension (or the aftermarket equivilent) is designed to handle up to the max tow rating, max axle ratings, and max combined weight rating, as long as you use the required equipment. That means a properly rated WDH. Without the WDH, you will (likely) overload the rear axle, and unload the front axle. With a WDH, properly set up, you distribute the tongue weight over all axles, and will not exceed any of the ratings.
Unless you are just dying to spend your money on modifications, there should be no need for replacing your shocks/struts until they wear out.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller