I won't comment on why some folks 'know better' when it comes to using domestic parts and appliances in an RV rather than RV-specific parts. Foolish is as foolish does and they will eventually pay the consequences. Whether it is a toilet, household refrigerator, domestic tankless water heater and the like. NONE are RVIA certified for use in a mobile environment, but ya pays yer money and ya takes yer choice.
As a factory authorized service center for both Dometic and Norcold, I can tell you that Dometic prefers to have all of their products serviced and installed by factory trained and qualified RV techs. That is the primary reason for their restrictive business model. They are doing quite well with it, BTW.
Thetford has other issues, like the HUGE recall now under way on some of their refrigerators, but they feel that they can exist with selling thru multiple sources, along with direct to the consumer. Their tech support is no where near as good as that of Dometic, nor is it really geared to talk directly to the consumer, but that again is another story.
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
SOLAR TECH ENERGY SYSTEMS, INC.
AM SOLAR ...MAGNUM…VICTRON ENERGY...LITHIUM & LIFELINE BATTERIES…MARINE REFRIGERATION