Yes this was a Dolly and something that was used in the early 50's mainly to ease noseweight and pitching, a chap in Yorkshire tried to market this but it never caught on. The idea was tried again in 1978/9 but to no avail however the Coventry Knight being towed would have been a real brute nigh on 2.5 tons- idea was you left it at a site and then it could be towed to storage after, now thats a good idea-wonder if it will come back!!! named as a "towable static holiday caravan" - shame I missed that bit of that show, only saw the last half hour must catch the first section up on caravans
Andy J