crib training - HELP!!

Shelby
I'm wanting to transition my 12 week old from his Rock n Play to his crib! Tonight was the first night and when I put him down he is totally fine... which is what I thought would be the hard part since he normally wiggles around when I put him down at night. lol The first time he slept for 45 mins then cried so I waited a little bit and then tried patting him to soothe him but I ended up having to rock him back to sleep. He instantly fell asleep and I put him back down (perfectly still again) and he was awake before I got back to my room and checked the monitor. So we repeated the same steps and he woke up again within mins. I'm rocking him now and he is sound asleep. I can tell he is exhausted so I may put him back in the RNP to let him sleep good. 
Does anyone have any tips??? Should I start by trying his naps out in the crib first? (Normally he doesn't nap in his RNP since that is his "bed") 
I believe the problem is he likes to be confined in the RNP. He was a NICU baby so he has never laid flat without having something confining him. But... he doesn't liked to be swaddled.