Try bringing something from his viv out with you, so he has something familiar as a starting point.
It's too cold here to go outside, but when I 1st let Maxx roam around the living room she did that. The I took her basking log out and sat it on the floor and put her there. She was much happier sitting on something familiar, and used that as a "base" to explore around. Now, she LOVES to be out of her viv. If she is grumpy all I have to do is take her out and let her wander around a bit and she is all milky white again.