How to remove the evaporator housing on Express G1500 Van

I had some damage to my 1999 Chevy Express Conversion Van. Unfortunately Bambi's mum decided to leap in front of me and promptly disappear through the front grille causing lots of damage to the rh side of engine bay.
The Battery was pushed through the plastic housing that contains the evaporator. I am stuck trying to get the housing off. Removing the cover of box, blower motor and evaporator was pretty easy. But not sure how to get the back of the box off. There are holes through the firewall and I have removed a two nuts from left of box and one from right. But I am not sure whether I need to remove the dash to get other bolts/screws. Any help would be greatly appreciated.