Great idea, I currently run embedded external apps in Road Runner that do basically the same thing. I just load each map as a separate app so the bottom half of my Apps list is all the different Weather maps. I also am a registered user of Weather Exchange. Their software ties together all the weather sat and radar imagery (including animated imagery), easy access to current local weather and 5 day forecast of any city, and automated weather advisory alarms together in a nice tight package.
Another site I like is http://www.wunderground.com/ where I borrowed most of my individual maps from. Somehow I was able to get web addresses for just the maps so all the surrounding webpage is removed on my carpc. Looks like the map is just another page of the front-end, very professional looking.
I never thought of it before, but I think I may contact the Weather Exchange folks with some sugestions for a CarPC version that gets coordinates from the GPS and automatically shows the nearest weather station data. This would be great for weather alerts too. If its pulling GPS Coordinates from the CarPC, when traveling cross country the weather alerts would track with the vehicle... hhhmmmmm (scratching head) this could be useful. Skinnable with bigger buttons would be nice too. I think I need to make a call on Monday.
Oh, and good luck with your idea, too