Yeah, so I thought the same about the PRV and the heat (its mid 30s here), however I pumped it up last night at about 10pm when the temp was down to mid / high 20s and it had gone limp by the morning - not flat but certainly bowing to the point where I had to duck to get out and pump it up again. This makes me think it's not a temp thing as it was cooler overnight and so in theory should still have been rigid....
So from what i can tell it has 1 inflation point with a PrV on the left hand side - which I've tightened, and on the right hand side it had a deflation point with no PRV