I think you can get 10 tubs with two sheets, if you don't mind a pieced together back.
first piece is 10x 16.75 x 24ish (going to be a little less from the saw blade). You should have somewhere around 11.75 x 48 after cutting (assuming a .125 inch blade) left over to use on the back.
Second piece would be 2x 72 x 24ish, then cut a 16.75 x 48 piece. That piece will be cut in half so you have your 11x pieces, plus an extra for the back.
What you have left over is somewhere around 7 x 48 and a 11.75 x 48. Also the extra 16.75 x 24.
Put the 7 and 11.75 together. cut one of them to make them 17.75 wide when together. If it is perfect it should be a piece about .875 wide being cut off. Cut this small piece in half to have 2x at 24ish. Put the 16.75 x 24 next to the 2x .875 x 24 and you should be over the 17.75 wide, cut to fit. Again if perfect you would be cutting a .625 x 24 piece off.
So basically you end up with a back that has a 5 separate pieces, but all covering the 72 x 17.75 inch area needed. Your only scrap is a single piece of .625 x 24, or less.
