The two tanks are held up by two steel shelves that are the most rearward components of the frame. Then the tanks are strapped in tight using what appears to be nylon belts. Everything else back there is an ash frame holding an aluminum skin which flexes something wicked.

So, technically, there is no rear steel chassis. The steel stops at the roll bars.

Getting rear ended is not advised...

What's your mileage? Who cares. Is it practical? See #1. What happens when it rains? You get wet.