Wow, does that actually help anybody? It seems like one of those mnemonics that's just as hard to memorize as the material itself.
I keep the RNA viruses straight by memorizing:
1. the -myxoviruses, rabies virus, and the wierd viruses that aren't likely to be tested (arena, bunya, filo, etc) are - sense and enveloped.
2. Remember one, the other one's the other one (i.e. all the other ones are + sense.) Now, you just have to take care of the envelopes:
2b. HIV is enveloped (otherwise I wouldn't have to remember all the envelope glycoproteins 🙂)
2c. All the MMR vaccine viruses (incl. Rubella = Togavirus) are enveloped
2d. So are flaviviruses
I highly doubt they will ask about icosahedral vs. helical. If they do, I'll just make an educated guess and move on with life.....
Hopefully either my way or the OP is useful to somebody 🙂