my jotul is 8 years old, had only door seal once. the "register plate" is 2m x.75 x.225 thick concrete the fireplace about 1 ton stone ,good burn in the evening then the whole mass stays warm all next day
this has probably been said before, but i,ll say it anyway, slight curve on the blade on edges helps for edge joining of boards as its got some where for the glue to be. i am only relaying what i was told by an old shipwright 50 years ago
i used 2 or 3 pieces of 25x8 steel rebated into and screwed across the underside of the cill leaving a margin on the outside edge that shows underneath
i thought the fire bricks at sides and front were to direct some heat forwards and how do you get a " good" draw in a bungalow, i am quite satisfied with my jotul, in six years its only needed rope seals. but i only burn seasoned logs though