Stephen,
Put the battery in the boot. Put the effort in now you wont regret the decision.
I cooked two bateries under the hood. I put the battery in the boot last year and wished I had done it a couple of years ago. My engine temp dropped heaps due to the air flow also.
I have bought a Rocket 550 CCA battery (it is a standard size) for less than a standard commercial battery. It turns my old Clevo easily, even when she doesn't want to start. Here's some pics.
Cheers
TC