Having had both Timbrens and Airbags, I prefer the airbags for trailer towing. I had the Timbrens when I owned a large slide in truck camper that weighed 5k. The Timbrens did prevent the truck from dropping as much as it did with the truck camper and prevented the side to side sway better than the airbags, but they may be too much for the pin weight of your 5th wheel. Unloaded the Timbrens did not affect the empty ride. I have airbags on my truck now towing my 5th wheel. I only run about 30 psi to assist the springs slightly for the improved ride on some of our rough hiways. They only raise the truck about a half inch at this psi.
Another option is the TorkLift Stable Loads which allow your upper overload springs to engage earlier, which will prevent some of the sag in the trucks suspension. They can be cut to size so that the upper springs are not engaged empty so you keep your factory unloaded ride.
Rich