Mine was not difficult. But I did not have a center board between the doors. Just removed the doors and no other cabinet mods. And I found a drop in fireplace from electricfireplacesdirect.com with dimensions that were almost exactly the size of the opening.
Things I did.
The fireplace air intake was on top of the cabinet enclosure. But I wanted the intake grill at the bottom rather than the top, so I built a base to raise the fireplace to the top and allow an intake grill (that I made) at the bottom, the air go around the side of the fireplace, and enter at the top.
Since mine was such a near perfect fit, I only had to buy some basic trim wood from Lowe's and cut, fit, and finish to match the cabinet.
