1/8 inch hole.. AND to reduce water entering light housing..
I use clear synthetic grease, around body where lens make contact, and then install lens. wipe off excess.
I was lucky, no wall damage. I had to replace all 14 side marker lights (running lights).. fading/cracks/water.... 10 year old trailer.
but for Base to Wall, any good exterior sealer. not the poor gasket stuff that came with original.
2012 Ford F 250,"XL" 6.2L Gas, 2 wheel drive. 156,000 miles
2005 Coachmen 29FKCS, Front Kitchen... 2005 Honda VTX1800F, 78,000 miles
N.E. Ohio in the Spring, Summer, Autumn.