Colchester Mastiff. Mascott Coolant tanks, rusting, replacement, sealing.

[Lanza]

I currently doing some work on my Colchester Mastiff and I have the oil tank out. This machine has a dry sump and the pump sucks it up from the oil tank. The coolant for the machine sits above the coolant tank. I have seen one of these Colchester tanks rust through before and there were some posts on the internet about it happening. The theory being that the coolant would help cool the oil.
Just wondering if anyone has ever sealed the top of a tank, with an epoxy or a product they use for sealing water tanks.