In California, be very careful if you are registered commercially and you go over 10,000# GVW. They include the trailer weight if you have one. If you are over this weight you will need an overweight sticker, they cost more. These are those 15, 20, 26, etc.....up to 80 stickers that are on the side of commercials trucks. 80,000# is the heaviest one can weigh on US highways with out a special use permit. If you're over 10.000#, you need a 15 sticker, over 15,000#, you need a 20 sticker, etc.
The fine is $0.50 per pound over the listed weight on your registration. If it's registered at 8000# and you're carrying 12,000#, the fine is $2,000. Believe me, I know, I paid it twice on my work trucks, to the tune of 5K. Now I have all the stickers on there, but the yearly registration goes up by hundreds of dollars. (Also, stay the hell out of Culver City at all costs. They are the worst.)
All campers and RV's are exempt from this. If the combined weight on your rig, truck and trailer, ever gets over 10,000#, get it registered non-commercial. If you have a commercial truck you use for work and play, and you regularly go over 10,000#, I don't know what you would do except get the overweight sticker.
Also, note. If you do have those overweight stickers on your commercial rig, there is a zero-tolerance alcohol policy. Any blood alcohol count at all while driving a commercially registered vehicle over 10,000# in California is a full tilt DUI.
Take care.