I think if you want to go cheap...the best thing to do is get an indoor rated box (not water tight at all!) and put it somewhere well away from any liquid or if it will be under the rig, cover it (just like the march pumps) so the water is deflected away.
By no means is this to any code but it will help from the minor spills and splashes we tend to see every brew day. If I were doing this I would at least get the water tight buttons, switches, etc since those will need to be accessible and not under the "cover."
Again, by no means is this saving you from any kind of electric shock, short or any liquid + electric hazard at all!!!
"So we were slammin' beers in the church parking lot..."
"I'm much too young to feel this damn old"