I too am looking for a bigger tank or aux tank I can replace/add to my 2019 Silverado. Someone said 15 mpg towing a travel trailer, I almost croaked. I just returned from a round trip to Cali from south Texas and the BEST I got towing a 5000 lb travel trailer was 10.5 mpg on flat road with no wind. For the entire trip I averaged 9 mpg, 90% at 60-65 mph. On last leg coming home with a 10-12 mph headwind I got 7.7 mpg at 65-70 mph. I have a wind deflector on the cab of the truck too! For now I carry 5 gals on a carrier behind my trailer, just in case but it is a real pain getting it into the tank due to the flap at the inlet.
