Seeking advice to secure a GPS to a kayak deck

The waterproof spec that is used is a static test. Dynamic water pressure such as that caused by splashes, or by dropping the GPS into water, can easily exceed the spec, so the GPS may not be 'waterproof' in your usage.

I put my GPS III + in a soft water proof case and secure it to my deck bag. It works fine and floats, should it fall overboard.

I have a little Garmin GPS and I keep it in a zip lock baggie in my PFD. I find a bearing using the GPS then just follow the deck mount compass untill I have some doubts about where I am : That is rare. A friend passed on a marvelous Inuit quote. ' Batteries die , White man die!' A GPS should never be a critical component. I keep mine in my PFD and have a chart case on my fore deck for long trips. The compass in a fog or after dark is critical, the GPS is convenient and very precise. My best friend on the water does not own one and he tells me he has never been tempted to buy one. I lost a water proof VHF radio while it was in my chart case on the deck. The chart got a little damp but the radio just died. It was warranty; buy if I wanted to scream Mayday into it that day I would have been out of luck.

My GPS sinks in the bathroom sink as well but the zip lock bag that is held shut with duct tape and has a string to my PFD floats nicely. My VHF ( Atlantis) is now in a dry bag kept in my day hatch. or in a dry bag behind my seat depending on the boat I am using. Good luck