Not sure who picked out 21 ft or why? 20 ft barely takes more than point and shoot. Inside of that, don't even bother with sites.
With very minimal practice 30-40 ft on a person sized target should have very reliable hits.
I think people have an image from the media of "drive by shooting stray bullets" that go into houses, windows, whatever. But those are careless and intentionally reckless and harmful wild shots by criminals. In reality it is not the case, when involving those carrying for self-defense.
Carrying a firearm in your camper so you and your family can be safe and secure is not any big deal, IMHO. As long as you are not a "prohibited person" (which is a net that snags far too many people, IMHO).
Be smart, keep your wits about you, and have the tools you need to protect your family. It's really not any big deal. Unfortunately it is the extremists who get all the media attention such that the average person gets a very distorted view of the whole thing.
A: Not everyone who carries a firearm is a nut
B: Not everyone who chooses not to carry a firearm has a panic attack if they see a poptart shaped like a gun
That's the true reality of it.