First time cooking Ribs. St. Louis Style, membrane questions + more
The membrane will inhibit flavor penetration but not stop it completely. If you have the chance you could pull the ribs out of the marinade, peel them, then put them back and they'll get a bit more flavor. Otherwise peel before you cook them, you won't make anything worse by doing so. 

As for the basting, there's a lot of opinion on this topic. Personally I've tried more basting and less basting and I've never found benefit in basting more than an hour from the end of cooking. The ribs have a lot of juice in them, basting them isn't going to keep them any more moist, what you are trying to do is impart flavor by building up a coat of the marinade/sauce on the outside. I've found that basting every 10-15 minutes in the last hour seems to give as good result as basting longer, and it's less work.