Bam ba lam, thanks for the information on a perplexing accident. The seat bases do not normally bend under static loads, they are part of the crash structure, so I would suspect that venting was related to a difference in pressure on closing the container and that at altitude. The ignition source would have been a major part of the investigation; the normal wiring system is pretty well put together on the RHC product, but in the vicinity of the rear seats there are a number of earthing points, and some live power services. The governor system sits back on the front side of the firewall, and that would be a point of interest. The RHC seat belt latch requires a greater throw than a car latch; if debris was projected forward from the rear between the seats, it is always possible that it impacts the latch on an upward trajectory and releases the latch. I have not come across any rotorcraft pilot that would undo their belt voluntarily, and any attempt to do that airborne single pilot is going to be a risky venture, much less so in a 44 than a 22, but not a good place to be.
An explosion sufficient to put the pilot through the windscreen, centered behind the pilot is probably going to compromise the flight control system which runs just below the floor in that area in its tunnel. One way or other, after such an explosion, it is not going to end well.
The Helipod externally mounted cargo pods give some way of carrying additional fuel, but it is always going to have an increased risk.