I hope this helps a bit. My wife and I have been full time RVing for 4 years now. We drive a 40' diesel motorhome and tow a jeep wrangler. We use a Garmin 3600 Palm, with a 1 gig SD card. With the SD card we are able to have about 75% of the US map available all the time, plus P.O.I., services, etc. The portability allows us the ability to use it in both vehicles, plus while geocaching, and it does talk to is. It is very user friendly. Anymore questions, just ask.
Team....Dave & Carrie