Warn SDB 160 (dual beam) behind grill mount

Here is my problem - question follows

I had a pair of Warn SDB 160s on a previous vehicle and they were everything I expected and were mounted in an upright position. I have a new pair and going to mount them upside down behind the grille - using elusive element light bar. I rotated the lens 180 degrees as required because there's a hole in the rubber behind the lens that should be mounted in the downward position and the light would not work properly upside down. The outside housing for the lens has a 1" x 1/8" drain to remove any water from the inside. Mounting the system upside down would require plugging that hole (live in Washington State with a lot of rain) and drilling a new hole on the top, which would then be on the bottom to remove any water.

Has anyone mounted these lights behind a grille? If so, what was used to plug the hole (was it heat resistant) and did you drill a new hole? This would void the warranty, but the only solution - unless there's is another.