Hi, Happy Holiday.
Harveys Maps are a very good British made maps system that use their own details and data to produce maps aimed specifically at walkers and climbers in the UK. As such they are a very good product for use in UK mountain areas in additionally to regular OS maps.
Harveys use a very good waterproof paper which has the feel and texture of paper but is very tough and waterproof, as such chinagraph and lumocolour don't work very well, If you apply any alcohol to erase them it degrades the paper and lifts the print.
I've always used a softened pencils on OS maps, a hangover to my days of marking nautical charts, but I was looking at workable option to allowance colour marking/ notation on Harveys Maps.
I'll continue my resource and report back in due course.