Sealing PVC cage?

I ordered a pvc boa master cage online, and have it all put together. The instructions say to use pvc glue to seal the inside four edges of the cage floor. I thought pvc was waterproof? Or is it just for the security of the cage? :)

The edges where you put it together are not waterproof. You need to seal the seams.

I wouldn't use PVC glue, instead I would use silicone instead.