When I installed mine, I bought some 1/4" x 15' windshield setting tape. I found it at NAPA but they would only sell it by the case at like $135 I think it was. O'Rielly's sold me a single roll.
I had to stretch it to make the diameter smaller to fit into the groove of the housing. Once I had it into the housing I left the housings on my picnic table, facing upward to let the sun soften the butyl tape. I then put the lenses on. If the tape is too thick, it's difficult to get the new lenses to latch onto the housing.
There are a couple of gaps in the bottom edge of the housing and I noticed there was no factory sealant in those areas. I think they are intended to provide a drain for condensation. You may want to check yours to see how they're set up.
