Since he is already used to the bed there.. try to start putting him on it for naps. dont force him to stay there.. if he isnt ready to sleep there.. he wont.
I started my kids out with playing on the bed.. then had then lay down for bottles on their bed. And then eventually naps. then they told me they wanted to sleep in the big kids bed.
I started much younger though.. my son was climbing out of his when he was 14 months old.. and then decided to "keep the crib" for the new baby that was coming to live with us. with my daughters, I did the same thing.
Let him ease into it with no pressure or fights. start asking him where he wants to sleep. By now.. he should want to do what big kids do.. and want to sleep in it if you give him the chance. And when he does start sleeping in there unattended.. get a gate for the doorway, so he cant wonder at night time.
I always had the baby monitor on so I could hear what was going on but I had friends who used a gate to keep their kids in the room. Seems like a good idea if he is really active.
Hope that helps some.
W. in Watkins Glen
Mom to 3 kids
Korey-Mikel 16, Whitney 13 and Andrea 6