L.S.
Chances are they will go over nap mats at your MDO orientation. Ours said you could bring a mat or a fitted sheet for a toddler bed and a blanket (that's what we did). I too thought my ds would never nap for anyone else but he did. They all did. I don't think there's anything you need to do to transition him. The teachers are pros at getting other kids to nap so leave it to them and enjoy the time off.