Connecting another panel direct to the isolator would be the best bet.

Taking a wire from the other panel would be possible but would depend on the thickness/rating of the other wiring and or what your running in total and far as current draw and whether the wiring/fuse can handle the extra load.

Cheers

Thanks Paul. The 1 remaining switch on the existing panel has a 15amp fuse. So if I run the second panel off that and only use low power draw devices off the second panel, all should be ok? My isolator is mounted right at the back of the gunnel and accessing the wiring will be a pain in the arse! Alternatively, your thoughts in having a third battery (mounted in the cabin) to power the second switch panel, and hooking up a solar panel to charge?

As Paul said, the thing to do would be to figure out how many amps all your different devices will draw and figure out how many amps your existing wire can handle. Then run a new wire if the old one isn't big enough.

Easier said than done though, because you probably won't know what gauge the existing wire is or how much any of your existing devices draw.

To be safe I would run a new wire with enough capacity to run your new electronics. You will also have to run a new negative return wire.

I would think that would be easier and cheaper than running a third battery and solar panel.

Also if you want to put a battery in the cabin it has to be externally vented or a sealed type battery. If not you could have dangerous fumes building up inside your cabin.

I would not run another switch panel off that one 15amp outlet. Much better off teeing off from the power supply into the existing 6 gang panel or better still run another wire from isolator/battery.

I wouldn't be running a supply from your last 15amp switch to run a new multiple switch panel, as Paul has stated running another supply is best. If your main supply wire to your original switch is heavy enough (rated) you could jump of that wire, this also may cause electrical problems with other sensitive equipment, eg: Bait pump running creating feed back noise on 2-way.3rd battery and solar panel, might be easier option for you, but at the cost you could probably have the proper wiring done cheaper.

Thanks for all the great info guys! With all thats been said above, I will install another switch panel and wire it directly to the isolator. The current wiring is about 4mm which I believe is usually rated at only 15amp? Will be changing to 6mm wiring which according to the Bias boating website are rated at 45amps. 

Paul, ditching the current 6 gang panel to a 10 or 12 way is not an option due to space limitions on the dash, so will go with 2x 6 gang panels on the left and right of the steering wheel.

Thanks again for the useful info guys!