dryfly wrote:
My previous trailer had the spare up front under the trailer.  It was well supported and I was able to add "safety" chains around it and attach to the frame.
My big concern with a front mounted spare is if it ever came loose.  The damage as it bounced it's way to exit in the rear could be catastrophic.  The retractable hangers used to hold the spare up that are on most trailers are pretty flimsy.
  Let me see if I understand what you are saying. Your spare, mounted on front, comes loose, it will bounce around destroying 
your property. But if it is mounted on rear, 
your property is safe. The death and destruction that likely will happen behind you is not important?
OP, on level ground, park the front tire on a string. Pull that string up to the lowest point halfway between that axle and the rear axle of TV. Box above string? Very unlikely to hit it. Could you make a cage to hold tank up between crossmembers? Might need it hinged so could lower outside end to get it in/out.