Cowl Vent? How to clean

Not to hijack this thread but I think this thread is done any way. I have a question about a mod I did. I took out my heater and cut the vent box off. Then I scrued the one side to the cowl. I was not thinking when I did this. Now I have a leak from around the scrues. Any one know how I could seal them but still be able to take them in and out?

Thanks for your help guys.
Russell

rubber washer and plumbers tape, maybe IDK just thinking out loud.