Where the plastic camper roof meets the body of the 1980 vanagon, right
above the front windshield, the seal broke (cracked).  So to make it
drivable without blowing the top off of the van, I used duct tape to
seal it, so air wouldn't get in there.  What is the best method for
resealing this and for sealing cracks in camper tops in general?
Thanks.

Don Schmeichel