My library is incomplete,and I've no peer-reviewed research which covers this specific application,so I'm a dead end.Sorry!
I have seen,at least once,a concept car (probably Italian)which had 'skirts',but where 'blisters' might have been,to contain the upper wheel/tire within the wheelhouse,they were left open.No wind tunnel data were given.
I suspect that a nasty 'jet' would be present while driving in rain,making for a dangerous visibility situation for any motorist wishing to pass.
Slower,higher pressure air under the truck would want to escape out the hole,perturbing the airflow right there.
