It can be super easy & cheap to make a frame that's easily adjustable and can work for a lot of sizes and any material.
Get 2 pieces of wood (these are 1x2's)- length needs to be longer than your biggest fabric measurement- and lay them parallel to each other- as far apart as the shorter measurement of your fabric.
In the photo, these are the east to west pieces.
It's good to rinse out your material and let it dry first, any organic material will absorb water and then shrink as it it dries- even PFD.
Notice how the crossbars underneath are outside of the fabric area.
BTW, elmer's blue glue gel works great as a resist. Just remember to let paint cure before rinsing out, a week is ok, 2 is better.
I usually do the painting outside with the stretcher on a couple of sawhorses. If you're using a table, remember to prop it up at the corners to prevent the middle from sagging and touching the table.
It will most likely drip in the middle, be prepared.