There has been some talk in the past about methods of charging your leisure battery - this looks like a cheap, and proven, option.
http://cgi.ebay.co.uk/SELF-SWITCHING-SPLIT-CHARGE-RELAY-KIT-VW-CAMPER-VAN_W0QQitemZ200292832473QQcmdZViewItemQQptZUK_Campervan_Caravan_Accessories?hash=item200292832473&_trksid=p3286.c0.m14&_trkparms=66%3A2%7C65%3A10%7C39%3A1%7C240%3A1318
I'm sure there are alternatives - but it's all there. Sorry about the darkside connection:I
'Harvey the RV'
http://cgi.ebay.co.uk/SELF-SWITCHING-SPLIT-CHARGE-RELAY-KIT-VW-CAMPER-VAN_W0QQitemZ200292832473QQcmdZViewItemQQptZUK_Campervan_Caravan_Accessories?hash=item200292832473&_trksid=p3286.c0.m14&_trkparms=66%3A2%7C65%3A10%7C39%3A1%7C240%3A1318
I'm sure there are alternatives - but it's all there. Sorry about the darkside connection:I
'Harvey the RV'