The new "ventless" gas cans suck. I've got two of the self priming siphons & havent' had much luck with them. Not sure if I'm just slow or what but they take forever & then stop at some random time. I've thought about picking up some of the motorcycle cans but their too tall to fit under the tonneau cover on my Avalanche.
Get a small vent free can with a nozzle that fits your boat and will stay in place inverted. Cut the bottom out. You now have a big funnel. Take the nozzle of the vent free can off and pour into the funnel.
I bought 6 of these from the local cycle shop at 32 bucks each. I made the fillers my self. They are qty 2 - 3/4" hose barbs, 12 inches of 3/4" hose, and qty 1 - 3/4" cap. That list will make one filler. I bought the parts at Orchard Supply