Speaking as a person trained in electronics: I see only 1/2 possible problem with this, and that may be fixable (or non existant)
Motor homes come in two types for this post;
Those which have a simple battery isolator system, so the Engine can charge the house while driving... This will need to be disabled (NOTE you likely do not wish to just disconnect it, but disable it)
Other motor homes (Mine for example) have a Bidirectional Isolator (BIRD) and the house also charges the chassis.
You need to disable ONE direction on this kind.. And i can not tell you how to do that.
Why do you not want to just disconnect? Well most Motor homes contain a built in "Jump Start" device, (The button on the dash marked Emergency Start, Aux Start or Boost)
This often uses the isolator relay.
