Thanks everyone. I will go down the path of commercial / light truck tyres for the trailer.
At the moment I'm not concerned about using the same tyres on the trailer as the car as the car runs stupidly expensive SUV tyres. (I tow with a Subaru Forester XT... grippy tyres make it plenty of fun to drive around town)
I'm sure I'll one day regret the decision, but it's likely that I'll be stuck in the middle of nowhere looking for a car tyre, not a trailer tyre.
Yep, what you've posted is legit. I was bitten by this very same bug with our camper which was also fitted with standard auto tyres. One gave up the ghost in spectacular fashion enroute.
When having tyres changed out, techy asked who fitted them on the camper, told him manufacturer, I was told they should be shot as their rating was no sufficient for the camper. How's them for apples ?
Won't mention the name of manufacturer here.
Short story version, fitted 8PLY instead of 4 Ply. The PLY refers to thickness of the walls of the tyre.
These were placed on the standard rim without any problems and are a much better tyre for the job.