Hello,
Loving my new truck. I want to get rust-proofing done from a non-Dodge shop for $400. They are going to power-wash the bottom before doing the rust proofing. Should I have any concerns about that? I have heard of electrical issues when power washing engines from top. Any warranty voiding concerns? You think it is a good idea?

Thanks!

 

The underbody shield should protect the engine compartment enough from below that power washing shouldn't be a problem.

You drive through snow/ice/rain so it's not like it stays perfectly dry.

 

Yes it sounds like a fine idea IMHO. There is no sense spraying rust inhibitors on top of dirt, so the wash seems logical. Plus they can charge you for it. :-)
I'm assuming the rust-proofers have done this before and are careful around electrical components. I could be wrong so you might want to let them know you are aware of the possibility. It all depends on how much pressure they're using. If you blast it with a commercial grade washer at 3000psi or higher, there might be issues. A residential model at 1000-1200psi should be fine if they're not too aggressive.
As for warranty issues, i doubt it, again IMHO.