With the water in fuel issue, any ideas on keeping a 5g. plastic jug of diesel in the truck bed when we take the 5th wheel from southern N M to Idaho just so we don't wind up out of fuel 50 miles from a Flying J.
Should not be a problem as long as the jug is approved container for fuel and you can seal it from contaminates such as water or dirt. I would not worry about a fuel additive for just 5 gallons. Make sure you use the fuel instead of long term storage once your trip is complete.
Make sure that what ever container you use acquire, the spout will go into the fuel opening and allow you to dump t least 90% of the contents into the tank. If not, you may need to obtain a funnel also.
Diesel requires a yellow container, according to code. It should automatically come at that point with the narrower nozzle.
As mentioned above, fill it just before your travels and use it up immediately after. Diesel grows contaminants very quickly and you don't want to foul injectors because you let the diesel sit around in your truck tool box or your garage.
And by the way, don't store diesel in metal cans. The diesel dissolves the zinc from the galvanizing on the sheet metal, and that same zinc ends up plating the inside of of your fuel system. It's not pretty.
I carry 2 cans from time to time. I picked up the 5 gallon blitz cans from the big box hardware store. To help get the can empty and prevent spills, I found that a short 8 -10 inch section of heater hose fits snugly on the end of the cans hard plastic spout.
And, as mentioned, I always keep a ratchet strap on them to keep snug in the bed.