spare battery for Challenger

Jumper pack inder your seat or enev under the bonnet , its tight for a second battery , a friend did manage to do this , ill have a look monday to see were he put it .Venus Bay

I have the November 2003 challenger, a newer model, but same sort of room under the bonnet, also found it very hard to find products for it, but slowly making it better. Have a cargo barrier, TJM suspesion with slight lift, cooper st tyres, rear areb air locker, just to name a few mods. I'm looking for a good LR fuel tank, and bull bar. I have also found the TJm snorkel for the triton will fit the challenger. But back to the point, opposit Lock have a great duel battery system, put a new tray against the firewall, next to the charcole canister, and move the original battery to this tray, then they put a larger battery in the existing tray, about twice the size of the original. The only problem at this stage is cost, I don't have a spare $900 to have it fitted, does anybody know a cheaper option...I live in Brisbane Queensland.