wooden hidies

Hello, So I have some wood hides for my two sows, they like to do their business in them, a lot. So now they have gone mouldy by the look of them. I don't like the idea of plastic hides since they are chewers. Is there a way of stopping wood hides from going mouldy? A wood treatment that is...

I was interested in acquiring houses such as these but ZooPlus doesn't ship to the USA. Does anyone happen to know where else I may be able to find houses such as these? I adore the natural looking wood on them. I've considered making my own but I don't think the trees out here are safe for...