The main town and admin centre for the county is Paisley while the other main town is the county town of Renfrew.

Renfrewshire Council

There is nothing on the website concerning motorhomes.

Paisley - there are several long stay car parks. Saturday and Sunday are free. There is no height or size information.
Renfrew - Charles Avenue PA4 8RT - 150 spaces no height restrictions. Parkopedia.