The Aux Battery will be directly wired to the inverter,mounted behind the
driver seat on the cabinet .

 The cig lighters , will be wired into aux battery so a solar charger can
back feed the aux battery and charge it while camping.I have made a fuse
panel to feed the extra circuits that will be powered off the aux battery.

The inverter use will be for a microwave, that will have short use(5 mins
or less)...1200 watt is recommended. I am going 1800 watt for an upper
margin.

So my question . Is a 300 watt stereo amp to much to ask of the aux. deep
cycle battery going down the road , with the radio and xm unit tied into
the aux battery and a small fan to help blow cool air up front.

The aux battery gets its power from a 10 awg wire from the relay under the
driver's seat. Since the battery stores electrical energy ...that is why I
am asking this , if it were just a straight feed off the 10 awg wire the
standard answer would be no....

Has anyone else tried this??