I thought when they measure the over all length of an "other" they mrasure from tip of the barrel minus brake/comp/flash hider unless its wielded to barrel and then to the very end of buffer tube, not the brace. So wouldn't that make a folder ok?
Here is one; check out photo # 205, thats a 2.5 gal Rubbermaid can in the garage, if they have lawnmowers or other power equipment they almost always have gas cans as well.
Hit a few of these and you have more cans then you need and probably lots other stuff too.
Estate sales are great sources for old style fuel cans at give away prices.
Check out https://www.estatesales.net/NJ/Northern-New-Jersey for listings in your area.
Last estate sale I went to they had a bunch of them in the shed, I'm already well stocked so I didn't buy any.
I would suggest several 2.5 gal cans if you don't have the strength for the 5 gal. size.