depends what you want to use it for and how much you want to pay.
can get some incredibly compact special purpose batteries but you can only draw the current out slowly. useless for an inverter for example but fine for some camping lights.
does it have to be one 75 in that space?
do you have room for another elsewhere? it might be cheaper to use two 40A/hr
Nah didn't really need to be a 75a/h anyway. Was just for a 40lt fridge in a Ford Terrorist. The plastic moulding in the rear cargo area had a space where the bloke wanted the battery to go. (and yes, it's a cabin safe battery )