I have a TM and cant run cable to it, wrapped it last year in a camping 12v electric blanket but kept flattening the battery, cost me valves in the end.
Just been bidding on ebay for eberspachers but they are nearly all over £220/250 mark. Missed one last week on 215.
Rang around van dealers and van breakers to see if they broke BT vans as most of them have them in the back, couldn't find any but found a dealer in Essex who would take 1 out for me, wanted £300, tried £200 dealt at £235, including timer etc, but took me over an hour to get there, now have to find someone to fit it. He said most went to boat owners, if you think about it its a nice little earner for him in quiet times, hadnt sold a van all week he said, and had a yard full of them as well to prove it.
If you know someone with a BT van and a heater in the back, make them an offer for £100 quid or so, you never know they might not know the value of it.
Murky