When to image Mars?

[SpaceDave]

Hello all. I’ve tried a few times in the last month to image Mars but have had very little success. Although a decent size, Mars is very blurry and wobbly. I am fairly new to the hobby, but I would say it appears to be poor seeing conditions. 

I am using a Celestron 6SE and Canon 600D. I have tried 2x and 3x Barlow. I focus using a bahtinov mask (on stars). I used movie crop mode on various ISOs and exposures, stacking at least 3000 frames (keeping the best 1%, 2%, 5%, etc).

Is Mars too far away now? Or am I underestimating how rarely you get a night of good seeing? How do you find out when the best seeing will be?