If you can get to the macerator switch contacts reasonably easy, it would be a good place to start. Check for 12v to the switch with meter and also 12 back out of the switch with button pushed. If you have power there and out, you have narrowed it down to either wiring to the macerator or the motor on the macerator. Any of the Roadtrek macerators that have the manual knob are susceptible to water getting into the motor is submerged or heavily splashed as the rod goes directly into the motor with less than stellar sealing, unless they changed things on the newest models. I can't say for your model, but Roadtrek also put the macerators upside down on the Chevies, which could also be an issue if yours is similar.
Unfortunately, you may be in for a bit of work under the van or a trip to the repair shop if you do have power to the switch. Did you buy from a dealer with any kind of warranty on it?