Well, thanks to
@Hashtag ChamLife for helping me ID what the white tray I used for my build was, a plastic drip pan, not sure for what, but so far, I've had no issues with drainage. As for your drainage issues, as I said before, beware of the wood becoming waterlogged and rotting, all the seals in my original cage were good visually, but water managed to seep through the tiniest of cracks. I find with building an enclosure from scratch, the most expensive and tricky part is drainage that is effective, watertight and durable. I hopefully have that in my new enclosure.