Need to make 6 of these quickly!
Here’s my adaptation:
Use a long tail cast on to cast on 20 sts. (Leave an extra long tail for seaming)
Work 10 rows of K2P2 ribbing with no extra selvedge stitches added.
Work 34 rows of stockinette starting with a knit row.
Work 10 rows of K2P2 ribbing.
Cast off using a stretchy cast off. I used the surprisingly stretchy Cast Off.
Cut yarn leaving a long enough tail to seam the side.
Use Mattress stitch and your yarn tails to seam sides.