Hello Sailer- I had the same problem with our SOB TT,water would seep in between the red lense and white housing.The water would drip on the bulb and run down into the socket and cause corrosin eventually blowing the bulbs/both sides different times.
I pulled each lense and cleaned the sockets out,(trailer connector unplugged from the truck).I cleaned the bulb contacts with a very fine bronze bristle brush,I then put a thin film of G.E. dielectric compound in the socket and on the bulb contacts and put the bulbs in.I re-installed the red lenses back on the cleaned housings and ran a clear bead of silicon sealer the width of the lense about a 1/4 wide on top of the lense where it butts to the housing and down each side about 1.5 inches.This solved the problem.The dielectric compound should be available in any electronics store or Graingers.
I also use the compound in the truck connector socket and in the trailer pin connector holes.