Did you disinfect the moldy areas with bleach?
If it's pure polyurethane, in satin or gloss, it's safe for iguanas when cured.
But clear 2-part 100% solids epoxy works a lot better. There are no solvents to evaporate, and it's very very tough and extremely adhesive. It's applied to the stained surface and the raw surfaces.
With either product you have to coat every surface, inside and out, with multiple coats to make it water resistant.
Do you have a Tap Plastics where you live?