I've seen pix of various masonry firebox's under construction, but darned if I can find them when I;m looking for them. I'm thinking of modifying my offset masonry firebox to install a side wall C. I. access door and replace the hinge-up flat steel access door currently on top of the box with masonry slab of refractory cement. The interior dimensions of the fire box is 16" by 16" by 20" high. The hinge-up steel plate door works well to allow for a charcoal basket to be dropped in, but it is nearly impossible to seal. Anyone have a suggestion as to what size door to install where to buy it? The bottom of the door will be very close to grade and will have to act as access for both building the fire and ash clean out.