These 500ml food containers are 3 for $2 at Kmart. Just the thing for keeping the weather off your prop controller boards.
There are smaller and larger containers in the same range, varying in price from 4 for $2, up to a few dollars each.
The DIN rail is screwed through the bottom of the container and into the prop.
Even if a small amount of water leaks in the large hole will let it out.
Make sure you pre-drill the screw holes to avoid cracking the plastic.
The large hole was done using a 3mm pilot hole, then a step drill.
All of the holes drilled quite neatly with minimal clean-up required.
I doubt these containers are UV stable, but inside the prop they’ll be fine.