When I first picked up my Roo, I filled the tank at the station where the CAT scale was and weighed the truck before picking up the trailer. Then after picking up the trailer did the other 2 weigh ins after filling up again ( 2.3 gallons ).
Also of note is that the person working this scale said I got free "re-weighs" for the entire day. So I only had to pay once. Just use the same truck ID when you buzz in.
And about buzzing in... I'm 5'6" tall and couldn't reach the button from the cab of my 2500HD Silverado. Fortunately, I still had a snow brush under the rear seats from winter... #shortpersonproblems !
Mark, Jenny, Adam & Lucy
2013 Rockwood Roo 233S
2015.5 Silverado 2500HD CCSB with Duramax/Allison