Sealing around Spa

[Davenj]

I would like to seal the gap between the Kooldeck (light gray) and a spill over spa (fiberglass). The gap is less than a 1/4". Want to keep the dirt, etc. out. Probably steps also. What would be the best product to use for this.
Thanks,
Dave

[graciec]

I bought some white bath tub caulk/sealer and was going to try that around my step in spa......