SmartSense Multi use for an outside gate

I would probably go a different direction.

Get a heavy duty weatherproof contact sensor like the following:

Then cable it to a dry contact input to give you the zwave notification. You can put the RF device in the protective box as long as the signal still gets through.

Here’s the FAQ with a list of dry contact devices that work with smartthings:

FAQ: List of devices with dry contact input from external sources

Examples here: