Along this same subject, weight your rig. It's to easy not to do. Get the Cat Scale app (Weigh My Truck) and get it done. You don't even have to get out of your rig. There is never a line and it takes 5 minutes at most, less once you get familiar with using the app.
Download the app, set up your payment method then head to a Cat Scale. Drive up to the scale enter the location code that pops up. It tells you when to pull onto the scale and you get each axle weight on the app.. It also sends you a PDF to your email. Then park your rig our while you're tank is filling at the pump, walk inside to get your certified copy that will be waiting for you.
It's to easy not to do.
Something I didn't know until I used one is, it is several scales, so each axle sits on a separate scale. Regardless of your vehicle combo you should have no trouble getting each axle on a separate scale.
Knowing your weight will also let you know how much air to fill each tire.
I had to weigh my RV to register it, so when I hook up and load up my box trailer for our first trip, I'm going to weigh it all again and I'll be able to figure out what my tongue weight is and my trailer axle weight also what my total trailer weight is.