The town of Irvine is a new town and the admin centre of North Ayrshire. The Isle of Arran is part of this council area the largest village on the island is Lamlash.

North Ayrshire Council

There is nothing on the website concerning motorhomes.

The following are from Parkopedia with reservations.
Irvine - Cunningham House KA12 8XG - 180 spaces no height restrictions.
Irvine - East Road KA12 0AA - 160 spaces no height restrictions.

The following are from the North Ayrshire website. These are long stay car parks with no other information.
Irvine - Caledonian
Irvine - Harbour Road
Saltcoats - Union Street
Saltcoats - The Braes
Kilwinning - Woodwynd