Half-gallon jugs - how to seal it

I have several half gallon jugs I'd like to use for wine that I don't plan to age all that long (read: dragon's blood). But, how do I seal it so that it can age a little bit. That metal cap that it originally had just doesn't seem like a good option, even if I buy new ones. What do you suggest?
Thanks,
-m

You can buy solid rubber bungs of all sizes.Usually a 6 1/2 works on gal. and 1/2 gal's.

As Kim points out, a solid #6.5 stopper works on those jugs and so does the "Polyseal" plastic screw top. See link below.

http://labelpeelers.com/equipment/caps/38mm-polyseal-4-count/

While I'm not sure if your cap is the same as the ones on my 1/2's, mine have a plastic insert inside of them that form the seal and come in contact with the wine. If you have that kind, they'll work just fine and you'll be able to lay the wine down on its side if you want to. I wouldn't want a metal cap touching my wine either. If you use the solid stopper (which is use sometimes too), beware that changes in temp and atmospheric pressure can push them out. You can also get the stoppers drilled out for an airlock and simply airlock your 1/2's if you like.

Thank you all!!! Sounds like I should go with 38mm Polyseal caps FTW. Would same caps work for 1.5L magnum bottles?