You can't have any air below the xd. Try duct seal -- it's 2.98 at Home Depot. It's like modeling clay, but a little sticky and waterproof. Just lay some down inside your kayak and press the xd firmly into it. Add some more duct seal around the xd to hold it in place and your ready to go. Takes about two minutes and is a lot easier and faster than Goop with no worries about bubbles.
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