I have a 8 mo. old male veiled. Exact same thing. If I ever figure it out, I'll let you know! LOL.
On your next visit outside, if you can find a safe area to do this, let him roam around some. Put him on the ground and let him climb up on some things. You have to watch him close though. This helped my guy get used to the outside trips. I'm getting an outside cage together, so I can just put him in that.