Personally I'm not a fan of tarping, particularly fresh, catalyzed paint of any kind, but especially a more porous product like primer or sealer. I envision (without hard proof) it interfering with off gassing that progresses over time, and if it gets some wet in the area from leaks in the roof there's the danger of entrapping moisture under the tarp that will get into the primer layer. Tenting, where you allow airflow would be better..........more effort, but that's not a problem for you.