I used this:





It had decent battery life and picked up signal pretty well in my car. I think they are discontinued, but just search "GPS module" or "Keychain GPS" for similar units.

 

If its not rated for "outdoors", I would not leave it uncovered. Won't hurt to put it in a plastic bag.

 

I use my Droid on both mountain bike and trail runs, I put it in the Amphipod Rapid Access pouch (sm) to protect it and I put all of that into a rear jersey pocket and use MyTracks and I pick up GPS fine.

 

I hike in the woods and map trails using my tracks. I keep my droid in my pocket and even on rainy days I have little problem with accuracy. My advice would be to just go out and try it and see how accurate it is for you.

 

It doesn't need visual line of sight necessarily. It can get a fix through certain materials. Again, just test it out.

 

that little pouch I mention above I often wear on my chest on the sternum strap on my camel back and while mountain biking I am slightly bent over.. no problems.