Propane smoker in a file cabinet - want to make a wooden door.

I built a smoker last summer out of a 3 drawer file cabinet, with a propane burner for the heat and using AMAZEN for my smoke.  After about 9 months of using it, I now want to make some changes.  It works good, but it is tough to move items around if the bottom items are cooking quicker than the top.  Here is what it looks like...

This is the bottom drawer where the metal plate in the back sits above the propane burner to help maintain constant temperature and the smoke is done in the front of the drawer with my home made tube smoker.



This is the top drawer, and where it is a pain in the a$$ to move meat from one level to the next.


So, I am thinking of pulling the top 2 drawers out and putting a wooden door on along with wooden braces on each side that I can slide racks in and out off. 

My question is what kind of wood can I use for the door and rack holders?  Obviously nothing green treated.  Generally I don't smoke anything much higher than 250, so do you think that having the wood in there would be ok and not burn?  I have read not to put any metal covering the door because than that could cause a fire.

I figure it is cheaper to build it out of wood vs. trying to find some metal.

Thoughts?