Have I misunderstood something here? LPG tanks installed inside? Vented to the inside? I assume this "tank" is for running LPG stoves, etc.
I have a long range diesel tank fitted + the Diesel/Gas Australia system installed in my 92 wagon. The 34L gas tank is installed underneath in front of the rear axle on the RHS & inside the chassis (opposite the muffler). It comes with a fairly substantial protective plate around it. The system gives me a range of approx 1200+Kms.
Like a sedan with the tank in the boot. There is usually no air seal between the boot and the cabin, so it is almost the same situation as the tank in the back of the wagon.It is legal, you need the right sort of tank with a sealed valve box and you run a vent pipe out through the floor. Usually about 2 inches in diameter and all of the pipes and wiring go though this pipe too.