Visit the Electrical/Battery section for lots of threads related to the Lithium upgrade process and actual requirements. As an FYI, they are not LiPo, you don't want LiPo in your trailer...you would want LFP or LiFe batteries to assist on any searches you take on. There _many_ threads in
http://www.airforums.com/forums/f449/
Summary of actual requirements:
* upgrade converter/charger
* add battery monitoring system (e.g. Victron BMV-712)
* upgrade solar charge controller (possibly, depending on model)
* modify charge circuit from tow vehicle