Several people have relocated the battery to under the hood. Using a varied assortment of materials as a battery holder. You can do a single battery setup using a larger capacity battery (2015 Goldwing is a close fit and larger capacity 18ahr, over stock pioneer battery 12ahr)or you can install a dual battery setup, where you pick two batteries, which are generally recommended to be the same for longevity reasons. That has an automatic isolator a manual switch.
There is also the option of installing it/them under the drivers seat. Which frees up the space under the hood for storage/heater/power steering/3rd battery. You can stuff up to a 75ahr battery under there. I have an 55ahr Optima under mine because I killed the factory battery winching.
::Edited for specifics and spelling::