Angus wrote:As to length, ever seen a glider being towed down the motorway? )long white box 50 foot long
Well, not quite 50ft! The trailers are usually about 8m long. In my less clever days I have towed a glider behind a 205
(I spent 3 years gliding so looked into trailer law quite a bit).
If the trailer Max authorised mass is under 750kg (and this should be stamped on the trailer somewhere), there are no special licence requirements. Only other requirement is that it's not heavier than the plated limit for the car. The usual advice is that the trailer should be <85% of the empty weight of the car.
IIRC there are some obscure regulations that basically mean while a glider trailer with glider in can legally be towed (it's an indivisible load), the trailer empty can't. That may be gliding club myth though.
The only other caveat is that some breakdown companies restrict the size of trailer they will cover if you need recovering. It may be worth checking the details in your policy.
HTH,
Jon