I had a custom tank made by George’s Custom Plastics Inc
http://www.geocustomplastic.com/index.htm George did a great job on the tank
It was about 13 gallons, 3/8 inch thick and darn near armor plated. It cost $250 including shipping.
If you remove and sketch your tank, George can make a heavy duty copy. You may loose a little capacity because it may be thicker but it is a great tank!