Finishing stretch knit edges

I am modifying a piece of baby clothing by adding a piece of knit fabric with snaps to secure it in place for a wriggly baby (picture adding the tail of a onesie).  I have tried finishing the edge with ribbing folded over the edge but attaching the ribbing this way is very fiddly and does not come out very well.  I overcasted the edge of the tail on my machine but this doesn't stabilize or strengthen the edge quite enough.  I don't have a serger (hello? Santa? are you out there?).  I don't have a lot of experience with knits so I thought I would throw this out to see if there is some method of finishing that darn edge that might be a little easier & nicer looking that what I have done so far.

Does anyone have any suggestions?

Thanks,
Jen

There's not a whole lot you can do with it, if you don't want to lose the stretch.  If you haven't already attached the knit to the clothing, you could cut the knit wider than you need it, fold the edges under (I like to fold under twice) and hem the edges.  I do a lot of work with knits and have found that it helps to use a little spray starch and iron well when hemming, then use your walking foot and a slightly longer than normal stitch length to keep the machine from stretching your knit as you go.  Using Wooly Nylon in the bobbin helps the stitching to hold up better, too, because it adds to the stretch.

You could also try using your ribbing slightly differently, the way t-shirt neckbands are made.  Instead of folding the ribbing over the edge of the fabric, fold your ribbing in half, the long way, and place it up against the right side of the fabric, lining up the raw edges.  Then stitch and fold the ribbing out.  Does that make sense?  It's hard to explain in words.

THANK YOU.  I ended up folding the edges over twice, zigzagging, pressing lots along the way and using my walking foot.  I finally have straight edges that look nice.  Thanks so much for taking the time to reply.