The new RT fittings with the gaskets and seals are great for this application, along with a little bit of duct seal putty. You want to get rain in the light fixtures and switches? From the weather system that gets created inside the conduits that pass to the outside of this cooler, as the alarm guys might find out down the line. Sealing is required by 300.7(A)
I have seen light fixture jelly jars like that full from condensation. The colder it is inside, and the hotter is outside, add humitity, and you got a micro climate thunder storm.
"Well - I oughta....." -Jackie Gleason