My PUL covers mostly get used if we are going to be in the pram or the car for a long time as that is when you get compression leaks with fleece or wool.
I used fleece and minkee covers all the way to QLD and back. I dont use PUL covers at all blah...sorry I know personal choice but my boys gets red asap when we do so I jsut steer clear...and i havent had compression leaks at all