Many young people and people with young families tow caravans and trailers tents as they have a low tight budget. All surely know they do not have to MOT tow vehicle but they do legally have to have it roadworthy and those that don't would probably tow without an MOT anyway!
It seems that you that bleat "I'm prepared to pay" assume that anything that looks a bit tatty is illegal.
If all these caravans are such a danger and as they only have basic mechanicals why not a free MOT if it such a concern and HM Gov are really worried abou the safety aspect!
I gather that plenty on this site drive older cars, surely they should be off the road if they are not prepared to pay for the latest safety advances
I'm not serious, but get the idea.
As you don't have to have your cooker or fridge at home tested annually why should anything other than the basic running gear on a caravan and body work need checking.
Quite frankly if you are not able to check over a caravans running gear and adjust braking and judge that the simple chassis and bodywork is safe to go on the road, I doubt that you are safe to tow and capable of coping with changing a wheel.