Rebs slept in tents more often than not, and those tents were 20'x12'9" open ended Fly Tents.  Oddball flies aren't going to cut it at We Soon Got Proud, so if you want to guarantee some shelter, get your mess together and finish a Fly Tent kit.  Price includes shipping.  Make sure to include your address with payment.
https://www.libertyrifles.org/research/uniforms-equipment/confederate-tents