OT...
I would be the perfect renter for you. I'm only home 3-4 days a month, and those days I'd likely be right beside you in the garage.
I'm actually looking at buying an old Ford dealership close to home. There are two apartments above the showroom, and the service bay extends out away from the building so noise shouldn't be an issue. If all goes well, I would turn the showroom into a small business incubator, rent out the apartments, use the service bay, and turn the parts room into a small fab shop. Might take a while though, only getting to work at it for 3-4 days a month.
Back on topic...
I was online chatting with the Braille battery people recently. They have a line of lithium ion batteries that are very compact and light weight, and moving it up into the engine bay might work pretty well, especially in your case. They use the stock alternator for maintaining charge, but would require a dedicated charger if allowed to go completely dead. I asked about replacing our factory batteries with a smaller one in the fender well, he said it wouldn't be a problem if you drive it daily, or keep it on a battery tender. My car sits at the airport for long periods of time, I'm using a solar maintainer that I bought from Summit to keep it charged when I'm away. So far, no issues at all, even after being away for up to 3 weeks.