VP jugs and a Turbo Pump with auto shut off from Amazon is what I use to fill KRX, quads and generator. Simple cheap and easy.
Just put a spout on one of them and swap as you fill. They seal good enough to lay lay down when full if needed but will stand under the hard cover on my 2012 F150 with just a cap and no spout.I'm still looking for a good solution. I have bought and installed the little yellow vent caps they sell on ebay and some of the vented spouts actually work ok when the can is vented. I guess the vp cans will be my next purchase they just seem to tall to me to fit in the back of my truck with the cover on. Thanks u.s. government for keeping us safe