Popz

When buying fresh stock for my tropical fresh water tank it involves 8hrs travel by car. The fish stockist uses plastic bags for the fish which I then put in a soft cool bag. I lay bags/fish on the top of a prewarmed gel bag. I feel concerned about aeration, and is there anything else I can do to relieve stress?

Dino

No need for aeration.
Make sure the bags are filled 1/4 with water and 3/4 with air.
I have been transporting/shipping fish for decades and this is the method that works best.
Unless they are fragile fish or packed too many in a bag, they should be fine for a day or two like that.

COBettaCouple

Methylene Blue treated water could help some, but would not be totally necessary.