Hi Rich.
I mounted the battery on the ledge between the roll hoops. Using a plastic tray sourced from a tintop at the scrappies and two lengths of 6mm studding with a length of flat bar shaped to the top of the battery. The rear length of studding is fixed top and bottom through a hole in the ledge, and the front one passes through another hole and is bent at right angles so it can be removed for battery removal. The flat bar holds it all together with a couple of 6mm nuts. I also mounted the cutoff switch on a bracket on the ledge and covered it all in with a carpet covered ply panel clipped to the rollbars with terry clips.
Just my way of doing it! But it does free up the space behind the wheel arch, and give you so much more boot space for those LeMans/Show excursions