Fuel tank in bed of truck

I have a 60 gallon RDS tank in my 2016 Chevy. I just gravity flow from the in bed tank into the truck tank. The install kit had me cut 1 1/2" out of the filler kneck. Don't cut the vent line unless you want a mess! I just let it free flow as I drive. After about 100 miles the truck says it's out of fuel and the fuel gauge goes to empty then the CEL comes on. Once the in bed tank is empty everything goes back to normal. It lets me go a very long way having 96 gallons of diesel on board. I ran from Saint George, UT to Fresno, CA without fueling with my 31' Toy Hauler. Empty the truck got me from Fresno to Denver and still had a couple of hundred miles to go on the tank. Well worth it to me.

My brother has one in his 2014 F250 and says the gauge just reads full to whole time the auxiliary tank has fuel.