Pre Fab Fireplace Exposed Walls

[oak34]

I installed a slightly used pre fab fireplace last year and it came with firebrick for lining the bottom and 6 fire brick that fit into a metal tab (3 on each side) of the fire grate. Other than that there is nothing protecting the back wall and the sides are pretty much exposed as well. I have included pictures below. I am hoping that its up to code. The installation is up to code. I want to install firebrick all around the inside and behind the heat tubes for added protection. The only numbers that are legible on the metal plate are X389460 & B89689. I just want to make sure all is safe and want to extend the life of the fireplace.

If anyone recognizes the unit or can provide any info. That would be great. Pictures are below.