Re: Mod Podge Alternative (advice needed)
In my experience I have never used mod podge for aquariums, it is definitely use in crating for foam builds though but I do not seeing it being the best use here. What result is it getting for you that you could not get with silicon?
My solution would be ditch the MP and stick with lots of aquarium silicon. Spread a thick layer down and while its curing add sand or pebble or rock to it to hide the silicon.