The last time I did an afgan like this, I used a plastic hoop. It worked out fine. It was an old plastic hoop (the new ones have a funny ridge in the middle mine just had a stopper on the botttom of the inside ring).

Hi Michael,
I agree. I would use a plastic hoop when you are stitching on your afghan. I cross stitched a baby afghan many years ago with a plastic hoop and had no problem with the stitching.
A word of warning when buying a plastic hoop. BEFORE you buy one, while you are at the store, take the inner hoop and outer hoop apart and SLIDE your fingers around the inside and outside diameters of BOTH hoops to make sure you don't find a plastic "nub" (sharp, raised plastic area that can damage your material) and that the hoops are completely smooth. I would do the same on wooden hoops but I like the plastic hoops because they are easier to keep clean.