I wouldn't freeze formula
You also shouldn't make it up - it should be made fresh as and when baby demands. Take a couple of bottles of freshly boiled water with you and the formula measured out on a small tub. In this weather you want to lessen the chance of germs forming in the milk itself so keeping it separate until needed when out and about is the best way
Powder isn't sterile so an even better (and IMO much easier) way of travelling with a formula fed baby is take sterile bottles and a carton of ready made