Ahh.. Gotcha..
By the time its all said and done, its just as expensive, and a little less work to keep the Z55/Clones Air Rides than it is to convert it to Standard because of spring replacement.
Edit: I cant speak to the Nivo's mentioned above, I know nothing about them, other than they are more expensive.
Edit2: And with him pulling a trailer, he should want the AirShock in my opinion. It will help with squatting of the truck.
The Nivomats adjust automatically with no external hardware; yes, they're expensive but can be found on lower mileage SUVs at the junkyard. Generally on the NBS SUVs they're paired with a softer coil spring.
When loading down the vehicle, they need to be "exercised" for a block or two of driving; they sense and compensate for the load. Not saying they're for super towing needs, but mine work great towing a 3800 lb camping trailer. Some of the trailers use a WDH and the lighter ones not, but either way I've had good experiences with them. When I load up with heavy bags of stuff at the lumber yard they bring up the back end just fine.