Older Aquasports had a molded in fuel tank coffin with a removable lid. Sometime in the early 90s They did away with the coffin and went to a solid one piece deck with no hatch to save $$. They did however leave a molded in seam line where the lid used to be. This gave the factory, dealers and owners a place to cut the deck to access the tank if needed. (I've heard stories of even the factory having to cut the hatch to repair a defect) The advantage is if a clean cut is made it looks like it was made that way with no damage to the non-skid.
So you will have to cut your deck to get to the tank. Make sure you seal the edges of the deck core with thickened epoxy to prevent water intrusion. Also drill your screw holes in the deck over size, fill them with epoxy and redrill with the proper size bit. This will also help prevent water intrusion into the deck core.