With the help of a local blog follower I was able to get the platform, bolts and waterproof wood sealant I needed. I've got the holes for the screws drilled in the enclosures, preparing to bolt them down. After that, I'll apply silicone sealant around the tunnel rims and affix weights to the platform. That's basically it.Behind it: The plastic shelf I was trying to use beforehand. No place to screw things down, and not quite big enough, but it would've been cool looking. Ah well.
I have about ten days until I move cross-country. I can't deploy the habitat in such cold water, but I can have it shipped to where I'm moving and wait for warmer weather while I build the interior elements (like the clover garden). Nice to be moving forward, anyway.