If DIY is part of the game, then try the 4x4x2 inch plastic box with cover such as a Cantex 10008 junction box. It is $10.58 at Lowe's or about $1.50 more at Home Depot.
Drill a 22 mm hole (3/4 to 1 inch) in the cover center, for the camera cable, and use 8x32 brass or stainless screws to mount the camera. In the box base side drill a hole for a Connex 3/8-inch die cast zinc clamp-on connector.
For clamping, add a short piece of 1/4 inch ID split plastic tubing to protect the CAT-5E cable when the clamp is tightened. The hole on the left is a drain along with its use to equalize outside and inside air pressure.