I do quite a bit of stitching in the ditch, and I too lock stitch before starting/stopping. I stick to the default stitch length on my machine (2.5) because I find I forget to lengthen the length when I start a new session. And yes, there are wobbles along the way. Taken as a whole, those wobbles disappear when finished and washed. Definitely use a walking foot, and pin baste very well.