Ive had the same problem , even if the truck was parked and it rained, I had condensat issues in the passenger light only.
every once in awhile I would remove the water let it dry out and reinstall.
Well last week after I let it dry ,I taped off both sides of the seam and sprayed that FLEX SEAL along the seam.
It's been raining for awhile and there's no condensate
2012 F150 ECO SC 157" PLATINUM