I'd hazard to guess it will vary dramatically from state to state. I went into a Washington state casino and they actually had a temperature camera you had to get a scan and wear a mask but didn't ask about vaccines.
We printed out our Canada vaccine passports and put them into a plastic sleeve and keep it in the truck I can't imagine that wouldn't be enough.

Thanks Ray, I think you are right about the variation from state to state, we will have to do some more checking for sure.

I found this website, scrolled down to the list of states and clicked on North and South Dakota which told me that they are both listed as being vaccine banned which means they do not require vaccine passports to go into any buildings.

https://www.usnews.com/news/best-states/articles/which-states-have-banned-vaccine-passports

I realize your question related to 'compliance' with local vaccination proof requirements. But a more important website to monitor is here: https://covid.cdc.gov/covid-data-tracker/#county-view Having been vaccinated, you are obviously concerned about maintaining your health. Some areas of the country - such as the Dakotas, which have the highest level of community transmission rates - have relatively low vaccination take-up rates, especially so in rural areas of our country, which is where we RV'ers tend to visit. My suggestion is to not let a state's (or local county's) lack of proof of vaccination rules lead you to a false sense of safety. And welcome to the U.S.!

Here in lalaland (California) it even varies county to county. It’s generally no-mask in San Diego County but you must mask up in LA County when going out to eat or to the gym.

We traveled extensively in the last two years in our rig, which was delightful. Our rig is a 4x4 so we can avoid crowds which is our preference anyway. The more rural you travel the more freedom you’ll find, but with freedom also comes responsibility. So get informed and do what’s right for you.

Thanks for adding the info, its very helpful,

In some states, like Florida, it is illegal to even ask for any vaccine confirmation. I have mine in my wallet, but no one has ever asked.