What should I use?

 

What type are you using... This should not happen unless you didnt clean both surfaces before applying the tape... 3M works great... The grey one...

 

even 3m isn't strong enough.. I've JB welded my damn side skirts.. they had hard time sticking so I'd recommend some kind or silicone.

 

Go to a Glass Shop ( Automotive ) and see if they will sell you a tube of Urethane best thing for sealing

 

Use a clear silicone RTV; works great in areas where the tape lets go. Thats what I use; 3M tape isn't great in areas of high tension where kit parts want to pull up. Just silicone it and use something to hold the part in the proper position until it cures (ussually overnight).

 

^ +1

 

3M makes stuff called adhesion promoter, It comes in little packets and looks like a alcohol wipe.
You can find it at almost all the paint supply stores.
Clean surface first, wipe with the adhesion promoter pad and I guarantee the 2 sided tape will hold. It works and works very well. Just be sure its where you want it when you stick it down

http://www.sherwin-automotive.com/pr...?product=29021