Need T-top Advice

[TooFly]

So I need to re-re-anchor my t-top. I bought toggle bolts, from West Marine, that require a 1/2" hole and ~ 2" of clearance under the deck to work. I widened the existing holes to 1/2" and apparently hit the top of a stringer and stopped. Is it ok to keep drilling, use an allen wrench to clean out the foam in the stringer (if there is any) and mount the toggle bolts? Any other suggestions? I'd eventually like to replace this T-top so nothing is set in stone.

Thanks,
Paul