No Power to Dash/Chassis

Joeycockerspaniel wrote:
So I go out to crank my motorhome. Batteries are fine. House power is fine.

Define "Fine"

How have you checked both house and engine batteries? What are their voltages at rest and when you turn the key?

How long has it been sitting? Sometimes converter/charger can't charge the engine battery due to isolator circuit failure or other things.

More often than not, if someone says "fine" instead of a measurement, there is something to be learned about testing for failures- which help now and in the future. We've all been there ;)