This acid tank model was patterned after one I found on the Internet that was located at the Wilcox tannery. It can be seen at http://www.jonestownship.com/history/Collapse_of_Acid_Tank.tif
My HO model was formed from two small hydrocal tanks joined end to end. The supports were formed from wood. I added a dome on top using a hollow pressed metal piece of unknown origin which was in my scrap box. Since it has an open top I made a lid propped open for visual interest. There is an interesting wood platform on the prototype which I copied. I have seen similar platforms on other tanks so it is not totally unique. I added a figure, a small jug, and a sack to the platform, and a dirty rag on the railing. There is a wood ladder for access to the platform.
This completes the elements of my tannery. Now I need to install them on the layout, adding piping and scenery. Once that is complete I will post a few photos of the tannery complex on the layout.
I have decided on my next industry to model and am researching it and sketching a few ideas on what it should look like. I will have something on this next week.
UPDATE: In response to the question, to make and finish the tank supports I first coated them with sanding sealer then sanded them smooth. Then I sprayed them with gray primer and let them dry. After they were dry I painted them with sandstone colored acrylic craft paint - not totally opaque. Next I carved a few cracks. Then I gave them a wash of india ink and alcohol to age the supports and make the cracks stand out. Last I put on some very wet red-ish brown craft paint streaks. Hope that helps.