As you've pointed out, handguns are out of the question and, frankly, unless you're prepared to pull the trigger, you may just be arming somebody that didn't have one before.
Stop where somebody is minding the store. KOAs( for example) are located all over the US and most have someone on site 24/7. Order a free copy of their directory at "WWW.KOA.COM". Give them a call at your potential destinations, explain your travel situation and see if they have somebody on duty and awake 24/7 or an emergency number to call. Most all that I've stayed in just have one road in and out, and it goes right by the office. And there are other campers close by. Thieves also prefer multiple exits and no witnesses.
Nothing is foolproof, but in the long run its wise to make yourself less of a target than someone else.
Above all else, if it doesn't "feel" right, move on down the road.