STD magnets

Yaaay mine just came in the mail. When I send them, do I need something in the back to cover the magnet part? Also, do I use one normal stamp or I need more?

And if I need something behind the magnet part, is it ok if I just have a piece of paper with the hotel block information to cover the magnet part?

I put the hotel info in with some of them, but not all, and all of my magnets got to their respective places.

I also only used one regular stamp on each.