Nothing wrong with another dump truck.
I like the water tank in the dump box idea. A detachable tailgate, drop in water tank self contained with pump and spray jets. Just drop in, plug in and play.

And better yet, if you build a pond in the compound, you could draw water into the tank RC style!
All kidding aside, that truck would look great as a dump truck but I can see this becoming the 1/14th scale version in honour of your 850 complete with a scratch reg built lowboy behind it.

. Or maybe a end dump trailer?