I got this idea from seeing it in Dick Mason’s Coach at an FMCA Rally which he graciously showed me what he had done to solve this issue.

My Prosine 2500 draws a lot of standby power.  With just the parasitic power draws in the coach, it pulls about 5 amps of 12 volts.  That is 120 amp hours of battery used every day without turning on any electrical appliances.

I wanted to be able to dry camp more efficiently, so I decided to install a lower power modified sine wave inverter.  I had an 800-watt inverter which draws only about 1/6 amp on standby and converts power at about a 90% efficiency.  I selected one motorhome circuit which supplies the TV and satellite receiver along with several convenience outlets and installed a DPDT change-over switch.  In one position this circuit is powered by the main power panel.  In the other position, it is connected to the inverter. 

I have used this setup several times now while dry camping and it significantly extends my battery charge life.  Instead of the 120 amp-hours a day, this inverter uses less than 4!  If I need to use a high power device like the microwave, I can still turn on the ProSine and use it as long as needed, then turn it off again. As a bonus, my TIVO does not reset every time I shut off the Generator as it is always on the inverter and does not need to switch over.

My 800 watt modified sine wave inverter is mounted under the foot of the bed.  It is wired through an 80 amp fuse to the 12-volt fuse box main feed. 

Circuit Breaker Box
I used a short 12-3 extension cord wire and cut off the female end and attached the wires to one side of DPDT switch
I put an 80 amp inline fuse to protect the inverter
The inverter is tied into the 12 VDC main fuse buss which has a large enough wire to carry the load
DPDT Switch – One side operates that circuit as normal on the Prosine Inverter and the other side operates that circuit on the new 800-watt inverter while removing it from the Prosine so it can be turned off while dru Camping