Do what Gtsboy suggested though...keep the battery on a trickle charge. I use an Oddyssey PC925MJT in my R33 and it also [these days] gets intermittent use. But - so far - my battery has lasted 5 years cos its always hooked up to a solar panel and PR1210L regulator. I also wired in a blocking diode to stop night time discharge. I have a plug I use under the car and so every time I park it, I plug the solar lead into the car. The panel doesn't have to be a big one, a 5 to 10 watt unit will easily do the job. I use the same type of setup on my bikes, my excavator, and my mini dumper. The dumper has a Lister 2 cylinder diesel motor which has no alternator or generator so the solar setup was almost essential.
Before I did this, I was going through batteries every 12 to 18 months.