You will get a lot less of that if you follow the rule,
1 coat for every 2 days
It gives time to dry and gas off
I wouldn't advise setting the plane at the field in the sun, it wil get too much heat on one side and it will also get coated with oil from the planes flying, this can cause a mess when you try to put more paint over it.
Leave it in the hot car would be a much better idea. or if you have to set it in the sun make sure you flip it over every 20 to 30 min.
Randy