Decided just to buy an 80L polypropylene crate.... Internal dimensions are about 600x400x400ish mm so will fit the longest parts I currently plan to use and means I can do batches of smaller parts to save time.

It's wider than I needed, but I have designed a little PVC pipe cooling system which will eat up some of the volume... will just run cold water through it to keep the tub cool. Whether or not it's necessary really, probably not, but at least it takes a few litres of displacement out of the tank which is a few less litres of acid to deal with!

Cheers for the assistance chaps