I am confoosed when you say he wont brumate.
If you are keeping him outside, he will do it naturally.
It also depends on where you are. The further south you live, the longer the brumation period.
It is imporatant not to feed him before brumation as undigested food can rot in the stomach.
You really should know all this stuff already...but at least you are asking now.
I have a copy of Keeping bearded dragons that I no longer use, you are welcome to it if it will help.It also has some good info on outdoor pits which may be of use to you.