Mapping on the Mini2

I was wondering if any of you folks out there have any experience using 3rd party mapping software in conjunction with the Mini, Allegro or other devices. I have spent considerable time boating and thought the Mini would make for one of the the most durable hand held devices for the marine environment. My unit was ordered with the on board JS navigator software which works fine as a single frequency course plotting device. I was thinking more along the lines of downloadable charts placed on an SD card and used as a hand held chartplotter. Any thoughts on this would be appreciated...