hello all, i just picked up a topper from a '78 elky yesterday and was wondering what to use to seal it si it doesnt leak? i used some foam tape that's for truck caps but there is a small gap between the back of the roof and the front of the cap. any thoughts?

I have a topper that was on my 1985 and it has a large rubber seal that has been RTVed around the lower edge where it meets the truck bed. Then they had used RTV around all the bed chrome also. I took the topper off and removed the RTV but it sure did not leak when it was installed.