OK, here is what we did. I wanted to limit the new trailer to be towed by '14 silverado 1500 as we use this for every day vehicle too. Wife found a Coleman 268rk model that suits us for floor plan nee...
The 80% thing came from another era when our LDT had 180-220 hp and a whoppin' 300 ft lbs torque if it ran right. Those old trucks had small radiators/trannys that ran hot/small narrow drum brakes/small axles/suspensions/etc/etc. So.... many folks suggested using 80% of the trucks capacity and it made made sense/cents.
Todays trucks have non of those issues and can run their recommended limits much easier/safer and a whole lot longer.