Leaving a cam and groove connection open invites dirt and weather straight into the seal. A 2" part v dust cap in aluminum is the simplest fix there is.
Size: 2"
Material: aluminum
Type: Part V dust cap, dust cap for an adapter
Cast, machined and assembled in the USA
Assembled with solid pins
Complies with Commercial Item Description A-A-59326D for quick disconnect couplings
Not rated for compressed gas service, including air and steam