I'd suggest you vent your ammo container too! :lecturef_smilie:
Sure, a
small amount of gas in a sealed container that has a bit of expansion space between the (frequently replaced) liquid level & the sealed tightly cap (like Mike's Tequila bottle.

) is probably
NEVER going to be a significant problem, especially if your small fully sealed container is itself stored/carried inside something that's not airtight; but once you start putting something that might vent or leak occasionally inside an also sealed metallic container that'll collect and contain the resulting mixture of air & gas fumes, you're actually half way to creating a cheapie but very effective bomb...

All you really need is an ignition source, like that tiny spark that you've never noticed which sometimes happens in the tail lights when you put your foot on the brakes; or the spark from the stone that your Spyder flicked up hitting/scraping the outside of the metal ammo box as it punched a hole thru it! :yikes: (Yes, both of those scenario's
CAN & DO happen! :banghead: )
So unless you
like the idea of something going
BANG immediately under & behind your rear end, ie, on the drawbar of the trailer that you're towing, then you
need to
either VENT the ammo container; or
GET RID of the ammo container!! :lecturef_smilie: The approved 'new design plastic gas container with internal flame arrester sleeve built in' would be better off simply on a tray & tucked behind a screen/protector on the drawbar rather than in a sealed (non-vented) metal container that
will concentrate any potential fumes &/or fuel/air mix inside a restriction box which will then concentrate any
BANG that might occur, intensifying the explosion! :yikes:
One of the worst ever 'off road incidents' I ever saw was the result of a sealed plastic Jerry-can/5 (Imp) gallon gas container being packed inside the rear of a sealed 7'x4' trailer with 2' high walls while the tow vehicle drove along a relatively smooth but dirt outback track. The slight but continual bit of movement that the plastic gas container experienced due to the track surface was enough to wear a tiny seeping hole that, over time, let enough gas fumes leak out of the gas container & mix with the air inside the sealed trailer to become an explosive aerosol mix that filled the sealed steel box that was the trailer... until the driver touched the brakes on the tow vehicle, triggering the trailer brake lights and supplying an ignition source for the 'quite large' thermobaric explosive device in the form of a 7'x4' trailer/56 cubic feet of fuel air mix that the tow vehicle was now hauling!! :shocked:
When all the dust settled, there was
NO 7'x4' trailer any more, just the ragged remnants of a draw bar hitched to the shrapnel blasted & completely destroyed rear end of the tow vehicle, and a whole heap of shredded food, clothes, camping gear, and trailer shrapnel spread for about 200 yards along the track!! Luckily, the 2 occupants of the tow vehicle were only momentarily deaf & a bit charred around the edges, but relatively uninjured - none of the shards of exploding trailer had penetrated thru everything between them and where the trailer had originally been, but there were some pretty large & sharp chunks of steel embedded fairly firmly and
ALMOST penetrating all the way thru the backs of the seats that were the last thing between them and serious injury!! They weren't even
just an INCH away from serious injury, it was
much closer than that!! :yikes: The tow vehicle (an expensive 4WD Wagon) & the Camper Trailer plus all the contents of both were basically shredded!!

pps:
So
PLEASE, don't put a gas container that might conceivably
EVER leak fumes inside a sealed/unvented box, especially not a non-vented steel box! :lecturef_smilie: