Parasitic Drain Dual Batteries Campervan

Hi all, I've just bought a van with camper conversion and the wiring is pretty amateur, obvious from the additional cables running directly from the battery, no isolation and a constant flat battery.

I was thinking of installing either a marine cut off to isolate the leisure circuit when the vehicle is switched off/stored or an audio blocking/diode setup. There is a leisure battery in the back for lighting and also feeds into a cheap and about to be replaced basic inverter. Though I haven't started on the wiring, I'm pretty sure the parasitic drain will stop the second I disconnect the additional ancillary wiring from the battery. My goals are mixed and any suggestions on which to address first and with what method would be appreciated.

1. Correctly isolate the drain using 'unknown' solution
2. Ensure both batteries can be charged with the engine running
3. Ensure the starter battery is in an isolated circuit to the leisure battery
4. Ensure the leisure circuit is optimised against idle draw.
5. Improve the amateur wiring at the battery so secondary circuits are professionally/safely installed and extendible.

<< Deleted orig Reply (myref 2015March02-6:37PM). Let me know if you want it back. >>

Depending on the alternator, I'd recommend a traditional alternator controlled relay battery isolator.
Voltage controlled aka marine isolators are generally only for stator systems or those with money that want to avoid finding or connecting the alternator's (regulator's) D+ or L circuit.

Search "uibi oldspark" for examples and discussions.