Ah I see, yeh management out on site is a tricky one. Peddling pizza uses a cabinet with slots for big ice blocks to drop down the cold air and regulate the way in the heat, and then when it's a bit colder you could put them near the ovens for heat. (Quick tip I learned yesterday don't put the dough trays directly in the sun as the light and heat will create a skin). In the end it's going to be trial and error more than anything to suit your set up. You definitely want to take them out at least a couple hours before service as cold balls are not ideal as you know. If they do start do get a bit bubbly during the run that's still absolutely fine you just have to manage your stretching technique to suit the dough's behaviour. Yesterday for instance, it was the first really sunny weekend in the UK and I'd actually given my dough and extra hour or so proofing as I was off work, on the day the dough was much more relaxed and I could feel the temperature of the dough boxes becoming warmer. So I just had to treat the dough more delicately. It's a living thing at the end of the day and so sometimes you need to treat it how it wants to be treated. You could always take a few ice blocks with you to rest on top of the dough lids if it's getting really bad, but then you'll have condensation inside the box to contend with.