Aha!
This is where it gets awesome. So, in my haste to pick up the trailer the ngiht before, I neglected to ask for the spare for it. Thus I was stuck, 15km S of Tarcutta, with a completely fucked tyre, and no spare. Oh and it was 9pm, tyre place in Tarcutta was shut. With luck maybe if I could make it to Gundagai I'd get something.
Very slowly moved the trailer up the road and to a rest area (about 300m total). Checked my phone, called some people, and managed to convince someone to go get the spare for this trailer, then drive it down from Canberra.
I have some nice mates.
Then, the awesome actually happened. Checked out my dodgy mobile broadband and... I had access! High-speed access (and with Optus, too; though I could have tehtered my Hellstra phone), too. Posted on a forum up here in Canberra, and, get a reply to the thread: "Mate, I live in Tarcutta. Anything I can do to help?"
Turns out he had an identical trailer wheel. Sorted. Drive gingerly back to Tarcutta. Seems the high-speed running had spun the valves open just enough to leak air. In Holbrook, both trailer tyres were @ 36. The non-blown one on the trailer was down to... 15. No wonder this one blew!