I see you have not had a reply and I can't help although some new tourers have a water or antifreeze central heating system.
You are probably posting in the right place but may have more luck in
http://www.ukcampsite.co.uk/chatter/display_forum_topics.asp?ForumID=39
I think it depends on how often you use it , how much you want to spend, a simple way to heat it would be 2 or 3 convector heaters on time clocks, how long is a piece of string?
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets