IMHO I think the odessey battery is the way to go. I have them in everything a good reliable battery is required. Race car. Sand buggy, airplane.
These will hold a charge for 2 years. Can be mounted on their sides. And has a 10 or 12 year service life
My race car was a pain to start, when we put 1 in I could not believe how hard the motor would spin
here is a link to read about them
<<http://www.odysseybatteries.com>>