You could also try sealing the base with silicon after boraxing. I did one last year. All I did was put silicon on some wax paper, set the dry base on the silicon, then applied more to the back and folded the wax paper over on it. It took about a week to set hard, but the paper peeled right off and it worked fine. Sealing is a good idea though, whatever you choose to do it with.

Here's a pic of one of my mounts from last year. Kinda simple, but it was the first one I made on my own, thought it was neat. The fan wasn't complete as I had a brain fart and pulled away the front feathers, which are the most colorful. I just put a new fan in it from this year and it looks much better.