On the question of caravan tyres, it seems quite common to fit "car tyres" on a twin axle van. I recently had to look for a new tyre and Swift confirmed that they fit "car tryes" (as in 4 ply) to their twin axle vans.
I do not find it surprising that twin axled caravans are fitted with 4ply tyres, as in general most caravans do not weigh significantly more and many less than cars, which manage very well on 4ply tyres.
Its only single axled vans where the load per tyre will be more, and that may require a stronger tyre construction.
Yes that was my understanding, certainly the tyres on our previous (single axle) van were different. Having "car tyres" on the van does make it easier to find replacements!