I had never come across this thread before now , but for those interested I thought I could possibly offer some sound advice after towing my wife's collection of living vans behind both military and classic commercials.
First thing to remember on early examples these were all on vacuum brakes , generally to the rear axle only , so once converted to air you still have only one axle braking. If it's a quality wagon on an Eagle chassis this can easily be between 8 to 12 tonnes , so stopping them is a factor.
Original tyre / wheel combination was generally split rims with 10.50 x 13 balloon tyres , like rocking horse dung today , but even when we could buy them not a practical tyre at over 30 mph , I can still recall a nightmare trip on a hot summers day with two blow outs on the m27 at 28 mph max speed. It was about 18 years ago the British Rubber Company started producing a low loader tyre option on a bespoke spun rim centre , money well spent then as peace of mind ever since.
Never let the tail wag the dog , so your towing vehicle needs to be ballasted heavier than the trailed weight , that's when loaded with your provisions for your adventure away. I always joke my family can add at least a tonne , when you include water tanks , wine and beer.
Speed on the road is not really an option when towing a 70 year old shed if you want to arrive with it in one piece ! 40 mph on modern tyres on billiard table tarmac is the best, but more like 25 to 30 and pot hole dodging if you live in Sussex.
Military vehicles make good ballast tractors , just look at what the showmen used when ex Mod surplus first came for sale., scammells , matadors , AWD , and diamond T's were favourites post war.
Long bonnets and long wheelbase vehicles are not best suited with some of the modern road layout's , mini roundabouts and ridiculously positioned keep left bollards ! I often leave home at 65' if I tow with the Constructor , but today's attitude with long slow moving vehicles has prompted some eye opening road rage at us , so be warned.
Cab over motive power , with power steering , all wheel drive and SWB with a rear winch would make a very nice vehicle to use here in the U.K, to tackle tight access muddy show entrances.