Dave have you checked the boot rubbers are not damaged in some way, I know from previous cars water finds it way in easily. Jaguar RFs are notorious for the same, my friends would end up with 2 inches of water in the boot. I fixed it with some sealant where the rubbers allowed water to get in. Our old Honda Jazz had a water issue in the boot, I removed the boot seal, and one boot hinge at a time, after carefully cleaning everything off with alcohol and drying off I sealed under the hinges and bolts with the sealant and refitted the rubber seal with sealant, the boot has been bone dry for over 2 years. This is known issue on a Jazz as well.

