It does according to their FAQ's if you click on the link on Page 1 of this thread. Well not free, membership costs £40 for seven days.
This is copied and pasted from the FAQ PDF
FAQ’s 3.1 What benefits are included with the scheme?
The Highland Campervan and Motorhome Scheme includes the following benefits which have been selected to enhance your visit to the area:
• Inclusive overnight parking at our network of designated car parks (See Map of Sites on the website www.highland.gov.uk/motorhome)
• Contribution to the Highland Restoration Fund which is designed to help support projects that will deliver nature restoration, safeguard wildlife, and tackle the causes of biodiversity loss due to climate change – this is initially set as 1% for every £100K of income generated
• Direct investment for sustainable tourism and to enhance visitor experiences
• An investment fund of £2.25M has been committed by the Council to improve existing infrastructure and to provide more Council owned sites
• Free daily access to showering and changing in any High Life Highland leisure location(external link) during normal opening