I use my iphone for this purpose with a mount/holder by Pro Clip
Pro Clip - a little pricey but you get what you pay for. They make ipad mounts too.
If you get a nav app which downloads it's own maps to take offline it does not rely on cell signal for this. You do need a cell enabled ipad to pick up location data though, even if you are not using data to find your location. I use the "Navigon" app for this and love it, but not sure how much it has for offroad trails. There are some running and hiking apps that have more trail data.
edit: I should take a picture of that with my new phone! Yikes!