We use a Garmin 4000 series in conjunction with the Garmin ETrex hand held unit. They both have SD Card capability and we use the SD Card loaded with ATV, Snowmobile and Off Road maps for travelling in the woods as well as use the Garmin loaded maps for highway use. We've found that a tremendous benefit is the GPS can tell us us which lane to be in for the pending turns. For example, there are three turns off I-20 going through Dallas connecting with I-35. 2 are right turns, one is a left turn from an 8 lane expressway. It seems that nearly every time I've gone through Dallas, it's always been "just long enough" to forget which is the left turn and I wind up either darting across 8 lanes of traffic or going 30 or 40 miles out of the way to get back on track. With the GPS, that doesn't happen. For the most part, if you're travelling the interstate system, the GPS is invaluable for turns and local information, on secondary highways, it will get you where you want to go, but you may find that it routes you through residential or high volume (narrow street) business districts rather than using the "truck route" which would be so much less stressful. Use it, but know what the map says as well.
As Festus2 says, a good GPS is invaluable, and if you're a member of Good Sam, they just announced a RV specific GPS system to augment their GS Rand McNally Road Atlas.
One item that I saw recently had to do with security of the GPS. If you keep it in your car, don't label home as such, apparently there was a group of thieves who were breaking into cars with GPS visible at football games, etc and stealing the GPS and the garage door opener. With those two items, they could program the GPS to "home" and drive right to your door, use the garage opener to gain access and they knew about when the game would be over, so they knew how long they had in your home before you realized there was a problem. Sly and cunning? Hmmmm If you get one, mark a place a mile or so away from home as your "return destination" and don't keep the GPS visible. It might just keep your prized possessions in your possession.
