You'll clean horizontal firetubes every 2 to 4 days, I think you'd clean the vertical surfaces of the wet baffles half as often.
And, you could make up a sliding rack, like a 'foos-ball' ? sliding bar, either with bars vertical above the bar, with
fingers up between the wet baffles, to slide over the surface of the baffle.
or like Harman has, a sliding bar above with 1/4" chain hanging from it.. have the slider exit the side of the boiler top
if you use hanging chains, or from the base if you use vertical standing rods.. just slide back and forth once a day.
The soot would land in the base, where the airflow reverses from down to up to the flue exit.. just build in a good
door with gaskets and latches, so you can open and shovel out the flyash.
All the above depends on your coal.. and how much air you have going through the fire. more air, pushes more flyash
up out of the fire, and up the chimney.
with a tall firebox like this gentleman Janitor, you can install the heat reflector like europachris did on his EFM/Hybrid