Gps
Stick with Garmin, any of the Garmins will be fine for your rocket.
I have had mine on my Rocket for 3 years and it still works great.
Try to find a Garmin model that has the ability to download routes from a computer, not all of them have that.
Also do not worry about waterproofing or any of that, its just as easy to put a baggie over the GPS or pack it away if it starts to rain.
Not worth the extra $400 for a waterproof GPS.
Mine is a Garmin 1670, they should be still available from Amazon.com , that was the cheapest place I have found them.