Steve I'm struggling with the same issues that you are. I removed my tank from under the seat/table area. The tank is in great shape but considering it dates back to 1975 I'm thinking its time to replace it. I do lean towards Ian's setup for many of the reasons discussed here.
The original tank was held tight against the bottom of the trailer with a sheet of 3/4" plywood and fastened with bolts. Seemed to work well.
The tank I removed is about the same dimension as the one you are considering.
This is the only wood that held the tank tight against the underside of the Boler
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