Hi Ben,
I'm an expedition style explorer/offroader too. I drive a Land Rover and run a website for offroaders in the Pacific Northwest (
Northwest Overland Society).
My company, Spatial Minds, makes Overland Navigator which is being designed specifically for backcountry vehicle dependant exploration. I'll try and post up more information in a day or two, but until then check out the website and let me know if you have any questions.
The product has large touchscreen friendly buttons, but is also very compatible with traditional laptops. All functionality can be controlled via user configurable keyboard shortcuts which is a lot easier than using the mouse touchpad to click on a small toolbar icon or open a menu. If you do want to use the mouse touchpad the big buttons are easier to hit when bouncing down a road. Instead of File->Open->Browse to open a GPX track, GPX tracks on a USB stick/memory card are automatically displayed when it is inserted. It has high contrast buttons and waypoint symbols, and a few other UI components that are different from traditional desktop software to make using the software in the field a little easier.
Regards,
Craig