Class A with tag axle - beware of $1000. fine in AZ!

well for what its worth, we fueled in Indiana with our motorhome on a truck island and was charged 28 cents a gallon above the posted price since we did not have a DOT number. Most likely the truckers are able to get a little better deal while the motoring public pays a bit more. Not complaining but just did not understand so obviously this is the last time I fuel in Indiana with a MH. Did not try to get into a car island but they may have similar rules. Any input from Indiana residents? tom