I think he's looking for a cool vintage look to water storage rather than just how to carry water in a tear.
But I agree with some of the ideas...bring it in a modern container and hide it in a vintage or vintage-look cooler, etc. Or pour it into a smaller vintage container when nobody is looking..
I can't think of a good answer. Vintage water coolers would be good, maybe one of those iced tea/lemonade containers (glass) with a spigot for drinking water. I don't mean a sun tea jar, but one of the nice ones on a stand. A 'southern living' type of thing...
You are going with a '46 theme? I'll think about this one. I take it you are kind of Deco Society folk. My trailer is kind of the same but, um, 70's! Vintage Melmac, tupperware, lots of woodgrain stuff (including the silverware), crochet blankets. Not that I don't like the older stuff..I do, but somehow when I was given the big trailer I fell into the 70's theme.
I'll do some searching and ask my Mom what folks did for picnics back then. Probably some kind of tartanware coolers.
Good luck! I totally get the theme camping thing!! See you at a meet sometime!!