this might not be wise incase you actually have to hit the brakes hard the water bottles might shift and pop the lid off and hi the eggs, ( now if it only like a single layer it might fine but not a entire lot of them .
if you got the room In the tub try this set the bottle up ( caps up ) and in side a cardboard box place the egg tub then set the cardboard box in the tub with water bottles around it ( box as a protector and insulates the eggs more if it breezy)