For about $110, I bought a Garmin Nuvi 2595LMT. I also bought a Garmin 78sc with marine maps for another $275. Add about $100 for two Ram mounts and a Glare Stomper and I'm still walking around with $200 dollars in my pocket because I didn't buy a Zumo 660.
I followed the instructions in this Youtube video to waterproof my Nuvi and can tell you (after I hosed it down when washing the bike and forgot it was there...) that the waterproofing works well. I ride in the rain often here in Oregon and the Nuvi does just fine.
https://www.youtube.com/watch?v=s2UvIoL78Cg
Whatever you decide to do, learn how to use your GPS. On longer trips, a GPS loaded with way points and pre-selected locations (like gas stations) will help you understand your options and make good decisions based on access to accurate information. Some features I use more often are one button to find close gas stations, one button to find a McDonalds (with free wi-fi), and quick access to all the saved locations and way points added before the trip. It's also nice to use Garmin's routing features to put together a string of cities, roads and way points for a planned ride. It's also nice to be able to talk to my GPS and quickly get through the menus without having to touch it. Of course, this doesn't work when riding your bike but it does work perfectly in the car.
The Montana and some of the other motorcycle specific GPS models will do what both of mine do but I'd rather have two units and find that each does its tasks more easily than one unit trying to do everything.