That sounds like a great idea, and the $20 for 4 sounds really reasonable!
Next time I go to Wally Mart I'll check it out.
You could even bring them inside at night if your battery goes dead.
We need to make some preps for the summer boondocking season.....our old trailer had one of those gas lanterns inside (as did our cabover camper) and that really came in handy when you were camping for days on end without hookups.