No the bowl won't last very long, especially ficus that can take a lot of water, and I doubt if the urethane will last either, though I wonder what the chemicals will do to your trees. Don't layer rocks on the bottom of plants - that's out of date, plus it's important to let water drain out, not sit around rotting the roots, but do use pieces of needlework canvas - "plastic canvas" available in any craft department or store. The bowl itself could last some time but the urethane seems like a bad idea.

The rocks on the bottom are large, and more for holding the large rock that the tree's are sitting on above the rim of the bowl. aswell as drain hole covers. I dislike the plastic mesh. The rocks are large enough to baracade soil from washing out, but they still will let access watter seep from the bowl. I was thinking that the chemicals from the sealer i used to protect the bowl might be harmfull so i was curious about applying bees wax, or some other natural substance to the inside. To further protect the bowl. and more importantly the roots of my trees.

Excess water needs to do more than 'seep' out. By the time it's finished seeping, roots can rot.