I'm with dieselbobcat. Carry the documents you need. Duplicates on the cloud. Create a folder on your email account. That way, you can access them from any computer in the world. And you're not having to carry a USB drive. Not reliant on anyone else. If your RV catches fire in the middle of the night, are you really going to track down the thumb drive? I carry too much **** in my pockets already. Don't need more!
I own a small "fireproof safe". I honestly dont' know if it would survive an RV fire anyway. I'd have to look up the rating.
I'm in the process of doing just that now. (Scanning)