Rear door for fire access

[splatgirl]

You will find that there is very little ash to deal with. Unless I am doing a big load of bread, I don't bother cleaning out the ash more than once in a while because there's just a tiny bit from each firing. My BIL who heats his home with wood swears it's easier to start a fire with some ash still hanging around...but who knows on that one.
To clean, most people have some kind of rake and shovel for ash and embers, and a brush for sweeping down.
A cast iron door will be a big heat sink. You'd need to figure out a way to insulate it. It would also pretty much dictate that your exterior finish is an igloo style vs. a house style enclosure unless you also want to mess around with making some kind of insulated tunnel from the proposed access door to the exterior face of the enclosure. Seems like a whole lotta work for, at best, zero gain.