More like what not to do, lol. Iceni John posted on another thread that one should buy quality plastic tanks and not build them with plywood. I agree whole heartedly, but is that what I did. Heck no, I did it my way.
I wanted my tanks in an insulated box, so I built a box for gray and black water tanks made of plywood, foamboard and epoxied fiberglass.
It's held up by twelve 1/2" rods, with six cross beams.
You know, this was my first major epoxied-fiberglass project. My inexperience lead me to use about three times more epoxy resin than I ever should have. That's why I say if it ever leaks it will be a very slow leak. Sawdust optional.
You know, I planned to put a baffle at least in the larger grey water half of the tank, but by the time I got to that stage I was over time & over budget, and was in a git 'er done kind of mood. I was also worried that the baffle attachments could be leak points, or that the thing would break away.
For anyone planning to do an epoxy fiber glass tank, fear the blush! Also, getting the colth to stay in sharp inside corners can be a pain. The stuff is quite easy to work with, kinda like welding in very slow motion.