We run Air ride on all of our service trucks. Took care of the sag from the crane mounted on one side.
If you can get the in cab adjustable controller that would be the ticket.

 

I had the Timbrens, they are OK, but they are not airbags. I installed a set of Load Leveler 5000 (airbags) and now I wish I would have done it sooner. Made all the difference towing my 12000lb Copper Canyon 5th wheel.

 

I also say helper air bags are well worth the money. You can fine tune them per your load. A add a leaf or over load spring will add spring rate and the un loaded ride will suffer. As for Timbrens, all they are is a over sized bump stop to reduce the travel your truck would drop with the added weight. Cheap fix if you ask me. All comes down to how much you are willing to spend. I can tell you going the air helper bags are not going to waste your money at all in the long run.

Hope this helps.

 

I have air bags on my truck and I would never run anything else...you can inflate them from 5-100psi depending on the load so you know you'll always have two things:
1) a level ride
2) same ride firmness/softness and handling regardless of whether it's full or empty.

If you leave them inflated while empty (even at 20psi), prepare for some saddle broncing because it is rough as hell. But it's easy to deflate them. Overload springs do not even come close to airbags, there's no competition.

 

I have air bags also, I've had a few sets now and will never go back to any kind of helper spring. Up here with the salt an sand in winter the adjustable helper leafs become unadjustable very fast....

 

That would be, uh, incorrect.

They are actually a progressive rubber spring. Don't knock it unless you tried it.

 

Go with a TImbren kit if you want to stay below $200, but you wont have adjustability from left to right, but does that really matter with a 5th wheel hitch? Theyre centered on the truck, and so is the weight. truck this link if i can post it right,

[URL="http://www.sdtrucksprings.com/timbren-suspension-kits/truck-suv"]

 

Here's a working link:
Timbren for Pickup and SUV - Rubber Aeon Springs for Chevy, Dodge, Ford, Nissan, Toyota