I purchased a 91 Chevy 1/2 pickup with a 7500 pound towing package. I looked at travel trailers, and bought a p/u rated to haul the particular trailer I was considering. The rear end of the Chevy squated quite a bit with a loaded trailer that was within specs, so I called Chevrolet and asked them what to do about the squatting. I didn't mind it too much, but would prefer the truck to ride level when loaded, for appearences, as well as the headlight aiming problem.
They suggested I have overload springs installed to offset the rear end squatting, but cautioned me not to over load the truck, as factory specs were finite, and overloading would void my warranty.
Rather than increase the weight of the trailer, consider air bags or overload springs added to your truck.
Evaluate the correct weight of the complete package and stay within manufacturer's guidelines.
David from jax