Scratch that, answered my own question it is labeled as Type 3 connector on the back! https://www.nema.org/Products/Documents/nema-enclosure-types.pdf
If you want anecdotal experience, I have no indoor/garage area to charge my Prime so I've always used the stock charger with outside plugs. I'm also not very good at disconnecting the charger before storms, so its been through snow, rain, sleet, ice, etc. So far, no problems except that the cord may need wiped down with a towel as it can get pretty dirty after a storm. That being said, probably the weakest link of the charge is where it plugs into the 120v socket. For safety reasons, I would only plug it into outdoor GFCIs and try my best to shield this end of the charger from the weather.
Good point and mine is enclosed (as per local regs). The trouble I found is that the box wouldn't close with the huge 120v connector plugged into the outlet and it needs to be closed for the weather protection to work properly. So I bought a 6in extension cord with a low profile, right angle plug. Unfourtunately, I couldn't find an outdoor version rated to 20 amps, so I had to settle on an indoor, 20 amps one. I haven't had any issues with this setup so far as only a few inches of the cord extend out of the box. It's held up well even under snow/rain/thunderstorms.
I had the same problem on a recent road trip where I needed to plug in my Prime to an outdoor receptacle (normally at home I plug in while in the the garage and the receptacle has no cover). I carry a 25 foot 12 gauge extension cord with me on the road, and I used this to make the connection. Then, stuck a 5 gallon bucket over the whole deal to minimize water on it. Pretty hillbilly, but it worked. The other problem I note with the stock charging cable is that the short pigtail between the plug and the control box on the cable is too short. if you plug into a wall socket on the road, there is no support for the control box. That also led me to use the extension cord so I could put the control box on the ground or under the car.
My controller hangs 100% of the time, whether in use or not. Since they put a short connector on it, I ASSUME they built everything to take the weight.
5 gal bucket isn't a bad idea, though I would probably want to elevate the cord off the ground inside the bucket to avoid water flow. Here's my setup right now: