Buy a good quality breathable cover. Tarps do not breath and will trap moisture. I would suggest putting the cover on for a trial fit and then mark the corners and/or any spot that will potentially poke through. Take the small pieces that come with the cover and sew them in as reinforcements before you use it.
I wish I had done this as I now have holes that need to be patched.
Good luck with your camper!
2010 Nissan Frontier Pro4X
Dave's RV Center, Danbury, CT.
"It's okay for a man to smell like bacon"