"Can anyone foresee any problems with this?
I have a 13.8v 10 amp power supply to take away - any problems with running 12v labelled stuff with it?"
Seriously your only going to get a whole lot of issues with that heating up
You will need at least this 85Ah deep cycle battery:
http://www.ebay.com.au/itm/12V-85AH-...item33a763764b