+1 for Delorme topo as the main mapping software for on and off-road. it's not perfect, but is one of the better ones.
i tried using some of the pre-caching tools with google earth and found it too much of a hassle to bother. instead, i can just pay $30 a year to Delorme to get unlimited downloads of satellite and Arial photography.
i use a laptop with a docking station in the back of the rig and have a small touch-screen and keyboard up front. i don't have any solution for back-country data, but that's not something i really need. if in a town i can use my android phone as a mobile hot-spot for the laptop to connect through, or i just undock my laptop and go into a starbucks and use wifi while sitting at a table to plan out routes and download any new needed data. my main uses of the system are bigger screen maps than most GPS units, factory service manual in PDF and other random saved vehicle-related documents, and OBD-II diagnostics. i eventually hope to upgrade my HAM rig and then integrate the APRS features with the system too (using Overland Navigator). more info on my still evolving setup is here:
http://www.mp3car.com/worklogs/1385...ition-vehicle-worklog-dockable-hp-laptop.html
oh and my screen has several inputs for cameras, currently i only have a rear-view installed, but plan to put front and rear axle cams to help me self-spot when i'm wheeling alone.