A.M.
I suggest you try adding some white noise and soothing lights - maybe one of those crib aquariums, a glowing stuffed animal, a light projector and/or a noise machine that makes ocean, heartbeat or another soothing noise.
My daughter has always been an amazing sleeper but when we go away for the night I ALWAYS bring two things - her "glow-y" bear and something to make white noise (sometimes it's a CD player to play lullabye music, sometimes it's the heartbeat bear, etc). The noise soothes her and blocks out other noises that might make her stir (she's a light sleeper)and the lights give her the ability to create soothing light if she wakes up and it's dark. She can light up her bear, look around the room and see that she's safe in her bed and fall back to sleep.
When I don't bring these items she has a hard time falling asleep. They make her feel comfortable and secure. She's had both a music/noise maker and some kind of soft light in her bassinet/crib/bed since she was born. Maybe adding something like these to his bed will help.
Good luck!