Not all kids are 'portable' nappers.
Both my kids, were not and are not.
They only napped, at home.
Not on the go.
But, for my son, when we went to a hotel on a long weekend, we got this type of thing and he napped and slept in it:
http://www.walmart.com/ip/Batman-Flip-Sofa-Bed-with-Sleep...
http://www.walmart.com/ip/Fun-Furniture-Flip-Open-Sofa-Ca...
And he loved it and slept well in it.
But my son was 2 years old at the time.
Mostly though, when it was his nap time I went back to the hotel room with him. And napped.
We kept him on 'his' schedule, per naps and bedtime.
So that, once we came home, he did not get all out of sync with his naps or sleep times.
Some kids, after a trip, will NOT return to their pre-trip sleep schedules/naps.
I don't know about 'training' him to sleep in a pack n' play... unless you only use that and not ever his crib, anymore. But that might just lead him to not sleep/nap, and will upset his existing sleep and nap, routines.
As I said, my kids, were not ever 'portable' nappers. Nor sleepers. And if on the road or in a stroller they would not sleep no matter how tired they were. Then they just got super over-tired and super fussy.
As the other poster said, pack n' plays, are not comfortable.
all the best,
Susan