For those out there who are doing their own tanks this link below has a wealth of information:
https://www.glen-l.com/phpBB2/viewtopic.php?t=28367
I have got back to work on the 23 SeaCraft project of my friends and will be building the tank for it from scratch. I was looking threw some sites to find information on best methods when building aluminum tanks and found this post. The guy really knows his stuff. Well worth the read even if you are just paying someone to build you one or just coating one you purchased.