caulk if for construction not automotive use IMO. to my knowledge caulk is not used anywhere on a truck or car when it's assembled.now silicone,seam sealer and various adhesives are. i'm not suggesting you use the same stuff they used on the windows but the butyl is actually for sealing windows and stays pliable/somewhat soft.
Amazon.com: Permatex 81730 1.5 Oz Flowable Silicone Windshield & Glass Sealer : Automotive
Amazon.com: Permatex 81730 1.5 Oz Flowable Silicone Windshield & Glass Sealer : Automotive
a.co
This what I used.