I would strongly suggest other ways. I haven't seen the you tube, but this is impossible to get right.
It will cost a lot. Say that the sub is 1/700 and its 100 feet down. Thats a brick measuring 200/700 feet if you add 100 feet under the keel. Or 3.42 inches deep.
If the sub is a Gato, the real boat is 311 feet long, add 100 feet each fore and aft makes 511 feet. 511/700 is 0.73 feet, or 8.76 inches.
match the beam on each side is 27 feet times 3, or 81 feet. 81/700 equals 0.12 feet, or 1.39 inches.
8.76 (l) x 1.39 (w) x 3.42 (h) equals 42.12 cubic inches.
On the Woodlands Scenic website their calculator calls that 28 oz.
Their product costs $ 32.99 for 12 oz, so three bottles cost $ 98.97.
One bubble will ruin your day, Pouring in layers seems to be preferred to avoid bubbles.
Visibility gets iffy.
If I were to try something like this, I've seen good results with a clear acrylic box with a "seascape" lid and the sub on a fine wire.
Just my 2 bits.
Bill