If it is truly glass-lined, you could have the same experience we did many, many years ago.
We had the idea of making a chimney by taking several of these heaters, cutting the ends off, and welding them together.
Torching a glass-lined tank takes quite a bit of effort. We ended up hitting and bouncing the outside to break the liner so we could effectively cut them.
We were successful, but that's the last time we'll try that. /forums/images/graemlins/grin.gif
You wouldn't have to cut that much, and I don't know about the plastic linings or the thickness of today's tanks, but the old ones were tough.
Just wanted to advise you of a potential snag to watch for...
-JC