I know there are plenty of WiFi dongles out there with SMA connectors (or smaller) but I wanted something sturdier and waterproof...
Step 1: Finding a Dongle and Box
I used a couple of old Microsoft USB wireless adapters. They seemed to have better range that the little stick ones and the little antenna on the case made connecting the plug easier
I used a PL-259 chassis mount because I had plenty lying around. N connectors would have been better but I didn't have any.
The case is a die cast aluminum box. Probably the most expensive part but that was a leftover from another project.
The little black antenna is just a hollow tube. There is a small coax coming off of the board. The center conductor is used as the actual antenna by cutting the shield back 1.2 inches. I shortened then soldered the coax the the plug.
Step 2: Waterproofing It
I used 3 screws and some #12 copper ground wire to make a tripod to float the board in the center of the box. Then I sealed the cable and plug ends of the box with some RTV and then sealed the lid on with more RTV. The cable already had a nice rubber jacket but you could slip a piece of aquarium air line over it and add more RTV if you want to be safe.
When the antenna is connected you can seal that connection with some 3M connector seal tape.