Timbrens would work fine if that truck saw an occasional load, but I think it would be a bit much for his plans.
Firestone bags are the best option. After having "passive" load bolsters (Timbrens) and bags, there is no comparison to bags. Not only do you have the ability to level the truck, you can also vary the pressure depending on load and helping the ride.
I have seen NB's truck, and it's the only one around that sits level to rear low on a daily basis.
Joe, get the bags. I'll even help you put them on. As far as the in cab control, I would skip it in your application unless you just want the compressor. You'll be maintaining quite a bit of weight most of the time.
BTW, Timbrens are extremely hard to beat in trailer towing applications. My dad ran them for years. But, I always felt it was like slipping a wood block in for a bump stop.
JMO
Dave