Newb looking for advice

Hi All...I'm a mason. Have been for 25+ years. I've built traditional fireplaces, Rumfords and masonry heaters....I've never even heard of these Rocket Stoves until there was an article in our local paper recently....now I'm hooked!... I downloaded Evans' book and now want to build one for our large porch/mud room addition....I have a couple of questions if you guys are willing to help...first off, let me tell you my plan...I plan on putting the burn chamber and all the exhaust pipe beneath the floor...I will put a couple inches of crushed granite...put reflective insulation on top...lay the exhaust pipe in several runs (25-30') then cover the entire area with crushed granite...put an inch of course sand and then lay some type of flagstone or concrete paving stone into the sand while levelling it...does this sound good?...my only issue, thus far, is that I would not be able to access the ash clean-out at the bottom of the feed tube or at the entrance to the exhaust pipe...Do I need to have ash clean-outs here? If so, any ideas?....I can put clean-outs for the running exhaust pipe at floor grade at the point where the pipe turns for vacuuming but I can't figure out how get the ash clean-outs in....do I need these? Any ideas how I could accomplish this?... also, I plan on covering the heat riser with a steel drum....put some ceramic wool around this and then go around this with some type of rock or brick...the wool is to allow seperation from the drum and to allow the drum to expand and contract...do I nee to do this or can I just put masonry around the heat riser...keeping the air gaps of course....I'm afraid of gasses leaking through the masonry....Is this even a concern? I just thought that the sealed drum would solve this concern and I think that the heat will slowly heat up the masonry ( probably granite )....anyway, sorry for the long post...I love this site and you guys rock!

as a start to answer your questions, the crushed granite you plan to use will need to be mixed with a clay slip to make it monolithic. I also used crushed granite in mark I and it didnt work well at all.
ash cleanouts...I thought, eh, who needs those. apparently I do. I am beginning to plan the Mark III currently and it will definitely include ash cleanouts.

the steel drum is called the bell. The function of the bell is to radiate heat coming up the riser. the heat in bell needs to be cooler than the heat coming up the riser, or else the drafting wont keep pushing it all through the ducting.

any chance you are in colorado? I am dying to change my english fireplace into a rumsford. Someday a masonry heater.

Thanks for your answers Rich...can I just pour concrete over all the exhaust pipe then or do I need clay?....if I encased the bell in stone, would that make the bell temperature hotter or cooler?....I will definitely incorporate ash clean outs....sorry, I'm in Newfoundland...I've been to Colorado lots of times though...once again, thanks for sharing you knowledge...

Did you manage with the RMH? We are considering a blend if RMH and Masonary, since your local-ish thought Id ask...