@Chadder, that is the nature of the beast when using vacuum cubes so you're not doing anything wrong. Any time a wall/ceiling/floor is opened/closed or a building piece is added to them the flooding occurs. Fortunately it only takes a second to use "drain all connected" to clear your base completely of water again.

Also, whenever I snap anything to the cubes, it also floods them

I'm having a problem when I open or close a cube thats not even connected to the ocean, it floods my base. Can someone help me?

@mcgwier I always appreciate a heads up if there is an issue with one of my videos, but you may be having browser difficulties my friend. Both of these videos are still up and fully accessible.

It would be nice if the videos were still there.

Yes, the Structures Plus mod is one of the best building mods available. One of the nicest things about S+ is that it's very compatible with most mods. So I used the underwater cubes from S+ (with their handy ability to "drain all connected"), and then added in components from the various other mods that I am currently using. It makes it just a flexible as building with your favorite mods above water, with the happy bonus of granting you excellent visibility into the waters outside.
I have a list of the various building mods I use in the video description on YouTube, but most mods work with S+ nicely unless they use non-standard size components. Thanks for watching Kitty!

How does this even work? I am amazed! Is this fully developed?

Thanks Kitty!

Amazing!

Thanks Typical! It only took a few days experimenting with it in single player. I did that strictly for the purposes of making this video, but it's often a good idea to try out a mod or idea in single player first before you commit a lot of time and resources on a multi player server.