Yeah I used butyl tape under it. I caulked over the ends of the plastic cover and when water got behind the plastic cover it pushed its way under the caulk and in around the window. I guess I should've caulked around the window first and let it set up before putting those trim pieces on. I now know that those plast pieces are not weather proof and will leave an escape route for water. Or at least that's what I assumed happened anyway.
On a seperate note, I can't believe how filthy the whole camper is! It looked clean but once I started scrubbing the walls and ceiling.... lol I can see just how dirty it was. The people we bought it from used it mainly to transport their entire family to thwir grandsons dirt bike racing so I guess they weren't all that worried about cleaning it! I seriously just wish I could be done with all the work on it! Ready to relax and enjoy it. At first it was a fun project but now it's turned into work ha ha