Yes, it could be a problem. But that’s the nature of DIY stuff like this. How well is it enclosed? If it is literally just right under the griptape and nothing else is acting as a seal then potentially there could be a problem if water were to ever sneak in there, but at the same time I don’t think any people on here have ever used griptape to seal anything off and much less have had any issues with water getting under it. The Evolve boards might be the closest thing to using griptape as a way to enclose the deck.