I would make a sangria concentrate and then add wine to the concentrate as needed.
How about using stainless stock pots to make and store the stuff?
Linda C

You can make big batches in a clean ice chest and refill jugs as needed.

If there's enough time before the date, I think I would buy those gallon water jugs and drink the water. Then I would make the sangria and use a new/clean funnel and put it in the gallon jugs. Should work out to be pretty easy. The garnish (chunks of fruit/green apple/oranges) I would store in tupperware and just add to the main container as needed.