Nigel replied:

The only real cranking batteries with cranking abilities are the spiral type batteries (optima, etc). Century has the Marine Pro range which have more cyclic ability than an average cranking battery, but they aren't a true deep cycle. There are also the switch batteries which are 2 batteries in one case (you can jump start by using a switch on the case), but they are expensive and don't appear to have any deep cycle ability.

Graham replied:

Remember the optima deep cycle can be mounted any where in the vehicle, even sideways if needed...etc.....Have seen them mounted in rear luggage area of Pathfinders, or behind seat in king/extra cab utes...
I'm having an optima deep cycle fitted to my caravan as it will also fit the Pathfinder if needed...(and can be carried in luggage area as a spare when doing trips like simpson etc..)

cya Graham