I too learned the hard way that isopropyl/rubbing alcohol will cloud a clear canopy.

All I use these days is denatured alcohol (DNA). It's cheap and works wonders on glow fuel residue. I went out and tested it on my gasser plane today after reading this thread and it worked very well there too. I haven't clouded a canopy with it yet, and it appears to not affect painted surfaces when applied on a rag.