Not sure where to post this, but here goes at my camp my holding tank rusted out from the out side in it also rusted one of the legs off. The cold water is the culpreate. I'm buying a new tank but this time I'm going to paint the tank with truck bed liner to prevent the tank from rotting out. this is the second tank in ten years what do you guys think?

 

If it is just a fresh water holding tank I'd see if it's available in either plastic or aluminum. If not I'd use Herculiner. It's like a truck bed protector but you roll it on. I would check to see if it is okay for that use though. I used it on my boat seats and it's still holding up after 5+ years.