Welcome to the Stovebolt cool
You can install a tank either inside the frame rail(check donor trucks at wrecking yards) or at the rear of the frame between the rails.
Look at the links and tech tips section at the top of the page here as well as other areas with more information than a person can handle in years grin

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
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Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!