The urethane will only hold up to the sun for so long. I may be a good idea if you washed them in some diluted bleach and water to get all the mold off again and respray them. I think I would touch them up every year with a respray of the polyurethane. The UV rays will break down just about anything. Just clean them again when you put them away and RESPRAY yearly. You could also just leave them without any spray at all on them. Gourds are pretty tough even without polyurethane. Once mold starts to grow under urethane, there is no stopping it. It just keeps on going until you have to scrap the poly off and re-bleach and respray the gourd.

That is my opinion anyway. Works for me anyway

I found if I use Patio Paints made especially to paint outside items, they don't mildew. Patio Paints have the clear finish also. They will last for years, I have never had them to fade in this hot Georgia sun.

aprilfool-where do you buy Patio Paints? Thanks

Aren't Patio Paints those paints that you use for your plastic furniture? Walmart carries it in spray cans..

The other option is to grow more gourds, ditch the moldy ones, start fresh!
You might also try a heavier, brush-on poly-urethane, like Minwax Spar. (also found in Walmart)

Jan