I have a Webasto Heater fitted to my 90 but I haven't had it working yet. I've got to sort out the pipework before I can test it so I'll let you know if its any good
craddocks surplus sell new used ones which have been pulled from discos - a while back when no one knew what they were i had a few off them for #30 each - now that people have worked out that they are quite handy they are selling for 200 +