I don't know much in regards to pressurised equipment so probably wrong but I thought the fact that the tanks were cylindrical had something to do with it's effectiveness. Also if you could/did pressurise a section of sill and then ruptured it while off reading wouldn't the resulting pressure release be dangerous for any occupant?
If I am busting through 3 layered welds and 3.6mm wall I think the rapid escape of 100psi through that split is the least of my worries, but having said that the pressure would be beneath the vehicle and there would still be a floor pan and carpets between us.