Here's a quick update. Miles came over this weekend and we finally got the tub laid into the frame. We put down a thick layer of concrete as a footer to support and secure the tub from shifting. It probably still will shift a bit after a few fill-ups, but hopefully not too much. Pressing the tub down into the concrete was similar to closing the lid on a waffle iron.
I got the drain pipe in too. Joining CVP pipe is way easier than soldering copper pipe.