Folks will say that if your meat is too dry for rub to stick,mustard is a paste-if you are in a hurry.Another approach by successful cooks would be to fill a wide mouth jar with wooster sauce and rub while at home and carry it to the comp.That way you have a moist paste to rub on the meats.
Remember ribs don't have the same meat to bone ratio,so you might not use as much.There are good cooks that trim their slabs up the night before and sprinkle heavy with brown sugar and let rest in the cooler/refrig.The slabs will be real moist the next day at cooking time and you can sprinkle on your rub the next day,as you get the cooker ready.
I'm still guessing that the moist environment of the traditional Cookshacks,won't benefit by spraying the rub OFF.
On big meats you can just add more rub to the moist exterior half way thru.Remember it can be easy to oversalt loinbacks.
Many comp cooks will coat their big meats with heavy rub and put back in the cooler for a few hrs.Then,while they are getting the cooker ready,they add another heavy coat of rub.
It is hard to overcoat big meats with rub.