I'm trying something: I got a Trekology single air mattress (about 4 inches thick when inflated) that started leaking around the seams after about a year. It's still an experiment in progress but I applied Plasti-Dip liquud paint-on to the seams.

I will let you know how it goes, but so far it sticks extremely well and leaves a thin rubberized like coating...

I used the Plasti-Dip 'spray' to coat some military Molle sustainment pouches years ago and it works extremely well to add a new water proof rugged coating that lasts. In fact I will upload that video here I made back then to show what I did...