I don't think I would use either filter. Just put a dew/light shield on the front of your scope and go from there. The OIII filter is a specialist filter that works on some nebulae and actually makes the view MUCH worse on most objects.
As for the moon filter, its not suitable as well.
If light pollution is a problem just limit yourself to the brighter objects........ Saturn comes to mind.
Good luck and have fun.
P.S. Use your cheaper eyepieces for public viewing definitely not your Pentax one.
I had one of these nights at Parramatta in Sydney. The skyglow was pretty bad and we had a lot of moonlight as well. Even omega Centauri looked washed out. Spent most of the night looking at either Saturn or the Moon, simply because this is what the public kept asking to see. You could also look at some double stars like alpha Centauri. I think nebulae will be difficult even with the OIII filter but you could try it for an experiment.
I clean my filter by blowing any grit off first, breathing some moisture onto the surface and then using a soft micro-fibre lens cloth. I think the coatings are pretty tough. Don't use any chemical cleaners.
Liz, if you want to view emission and planetary nebulae with higher contrast, I'd suggest you pick up an Astronomik UHC filter. These have ultra hard scratch resistant surfaces, and will increase the contrast on almost all emission and planetary nebulae.
- its a Knight Owl Filter #ND96-0.9 - hmmm .... think this is just a Moon filter.
