In my limited experience:
Writing on a Harvey map needs something that is waterproof and 'soft' e.g. wax pencils or permanent OHP markers work fine. Easy to remove with an alcohol wipe. The key point of course is to remember to remove nay marks made after use. I remember once spending quite a while looking for a boundary that was clearly marked on my map but on closer inspection turned out to be a fine black line I'd drawn the year before and forgetten about !!
Writing on waterproof paper should be possible with anything that will write on paper BUT I found that when using anything that was 'sharp' it was easy to perforates the paper so soft pencils rather than HB pencils and gel ballpoints rather than normal ballpoint pens - this of course could be down to the paper I was using!!
I have to confess I never tried to remove the writing from waterproof paper so I can help with that.
Ian