Quit beating yourself up...
...(Let us do it behind your back!!!)
...Just kidding, pal...
It's easy to get distracted and to forget to replace the fuel cap, but you will address that situation with the retaining lanyard for that cap ...and you will know what the fuel smell means if it ever happens again. Lesson learned ...no one hurt.
Mine is a locking cap without a good place for a lanyard. I place it on the first step inside
the coach so I will have to step over it when I re-board. Also, the cap will not release the key until the key is turned to locking position, so I just leave the key in the cap (along with the ignition key on the same ring) until it is locked down. Fail safe. (I need that.
As RVers, we operate a very complex piece of machinery under very dynamic conditions. We must develop SOPs and protocols (and lots of little tricks) to ensure everything is stowed, secured, locked down, and made fit for travel... at every stop ...every time.
...And then hope and pray we got it right. Laminated check lists are very helpful to that end.