It's always difficult to give the soundest advice posible when your not there and have the advantage of physically seeing the problem. What your going to do is great, your doing virtually everything possible to eliminate contamination...I do have a question...the paper towels your using, what kind are they, please don't say "Bounty" or "Kitchen Catch All"...that type of thing. The towels you use are very important and you need to use the towels that are designed for the job.
With the problems that you've been having, it may be a good idea to go over the surface twice with Wax and Grease remover...When your done, blow dry the area, let it sit for 20 minutes (just to be on the safe side).
Contamination has been plaguing painters since the dawn of when painting began. An old trick to stop wrinkling and minimize contamination was to spray a very light coat...a mist coat...over the suspect area, let it flash followed by 2 heavier coats for flow. The idea behind this is that the contaminated area would be sealed off or bridged...does it work? This technique has bailed me out of a few jambs in the past (mostly back in the lacquer primer days)...with all the problems it might be worth a try.
To every painter that has painted for any serious amount of time...it seems every once in a while that car shows up that no matter what you do problems, arise. You can't keep the paint clean, contamination, runs, blotchy color, poor flow...and...the next one turns out virtually problem free...Why? Don't know, it just happens and all you can do is minimize the chances of it happening again...get it done and move on to the next job. Just like a Goaltender in Hockey getting blown out in a 6 - 0 loss one game and he bounces back the next game and gets the win, so it is with painting. You have done a good job minimizing, I'm sure your going to get that win.