First off, it's a "shotgun approach" you'd need a lot to coat all the inside surfaces thoroughly, and how would you distribute it to cover your leaks? The rifle approach is better -- pinpoint your leaks and fix them with a patch or valve replacement.

Put some soapy water in a sprayer, pump it up hard and look for the bubbles. Most likely it will be at seams or valves.

If the fabric itself is actually leaking in more than a few specific wear areas you need a new dinghy.