using an invertor

[Thomas-the-Terrano2]

been thinking about using an invertor in caravan.

previously run it from a 12v 2 pin socket thru a
cigar adaptor. thing is if want to run several low
watt items need to use a multi way gang adaptor.

SO, what about connecting its 240v output back into
van's mains, ideally thru van's inlet which will then
give limited 240 to all sockets and presume benefit
from going thru the curcuit breakers.

further if an auxilery battery was in car and fed to van
via these circuits and subject to being well charged
would it be able to charge the van's inboard battery
via the van's charger. thinking that when on a non
hookup site/rally if go out in car the car's aux battery
will be topped up and save draining van's battery.