We used a tomtom with the Morocco maps. Pretty accurate and helped us no end. I doubt any UK sold satnav will have Morocco on by default, so you will probably have to buy the maps as an add on. Easy enough with TomTom.
Unless of course you are a hacker and have a, erm, different version of TomTom and can read any map downloaded off the internet. /apparently.
Also - Vicarious books Morocco guide isn't great, but it does have info about campsites including GPS - so whilst you may not use it much, probably worth having as (when we looked late 2010) there was nothing better we could find.