Mark,

I used striping tape (two layers). It's the kind that you get at auto body supply stores from 3M. The blue one is the thickest. (I don't recall the mil). Anyway, with two layers you can sand with 150# and it won't go through easily. The top layer will need to be replaced depending the amount of sanding. On top of that I used 2-3 layers of blue masking tape about 1 1/2" wide to protect the rest of the exposed plexiglass. After over a year of on again, off again work I didn't have any discoloration. As always keep acetone away from your plexiglass ALWAYS. Clean with soap and water or alcohol.

One more thing. with the transition "step", I added just a little flox in my micro to aid against chipping. The whole canopy came out very nice, but what a lot of work. Try not to go too far with the micro. The primer will do some filling and it's easier to sand and fair in.

Here's some pictures,
Don Barnes

http://www.lancairlegacy.com/09_03.html
http://www.lancairlegacy.com/07_04.html