I agree with Dutchman Sport. I bought a small safe a couple of years ago and thru bolted {quarter inch bolts with large ss flat washers and double locking nuts} it into the bottom of the closet. A thief could probably get it out but that would require more time, tools and noise than most snatch and grab thieves have at their disposal. If they want it that bad... have at it.
My safe, like many operate with a battery powered keypad but also has backup - key operated access. The key lives on each of our RV sets of keys and as long as the batteries are fresh we can always quickly/easily access the contents {among other things I keep my gun in the safe}.
Leaving a key defeats the purpose of having a safe in the first place. Unless your safe is fire rated for 30 minutes and not many small {inexpensive}, safes are, the contents will be toast in a hot RV fire. My large safe at home has a 30 minute rating and in our community the fire department has a less than 5 minute response time. Out on the road or in a campsite you will likely see your whole rig turned into toast before the first responders arrive.
If you are worried about having account numbers compromised you can easily disguise them. Add a few random numbers, something that you can easily remember, at the beginning/end of the real number and run them all together. Be creative and no one will ever figure out your actual account/ss/medical record numbers.
As always.... Opinions and YMMV
:C