I used an older Mardon as a doner van for suspension and brake parts for my last Thomson, some of the parts i needed where obsolete so was cheaper and easier to buy an older van and use the parts. Cost me £50 for the van and I sold of the bits I didn't need and made it into a towable unbraked chassis, got £75 for it lol! Cost of spare parts - Nil! (Who says us scots are tight! )
I've no listing at all for a 'Marston' and I've records back into the early 70's,
Normally caravan front windows percentage wise are split 30-40-30, the pictures show windows split 25-50-25, Mardon were the only ones to use this style so if you know that, their easy to spot.
It's probable each make has it's own distinct feature that sets it apart from another, in the 70' swifts low middle windows is another example and designed so you could see through while towing. As it happens I followed one of these in immaculate condition last Sunday evening.
A Mardon was the first van my Dad bought, a 'mini Mystique' it was, about 9ft long and under 6ft wide, narrow enough to get in the back garden by removing one fence panel !!
I will always remember mum being really excited and climbing in as soon as dad got it unhitched and opened the door, yes it tipped up!!
I have always liked the way that Swift had the lower windows giving better drive through experience. With Thomsons' it was the 'Boat Roof' so called because they used a similair method and shape used to boat building, don't know if they ever trying floating one on its roof though.
One of the other interesting facts about Thomson's is their claim to being one of if not the first to use wind tunnels to test their design.
I can imagine the look on your dad's face watching the caravan go see saw!