I understand people putting additional safety margins on total trailer weight, but never heard that applied to TW. A cushion on trailer weight is useful becuase that affects driving dynamics like stopping distance, etc. But TW is just to be sure you are not overloading the truck's suspension, stop or go. And the WDH will properly distribute that load between the 4 axles.
I think you are overthinking this. You have plenty of cushion.
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