Hi George. I know your pain when it comes to high-temp photography. The noise gets really bad. All the same you could probably make the subs a bit longer given you are taking darks. You will need a lot of subs to make the short subs work - like >100.
Try not to clip the black end of the histogram - it's left the edges of the nebula looking hard and ragged.
You might want to give it a reprocess and ask for more comments.
Good luck.
