Hi Wade; Welcome to Permies!
I second building a bell bench with no roof.
Brick sides with paver / stone top.
Now your J tube core and barrel I suggest a roof over it for snow protection and so you can use it during wet weather.
I suggest building an 8" J tube .
Firebrick construction rather than ceramic board.
Morgan
superwool for a 5 minute riser.
A 55 gal barrel with a removable lid.
Firebricks for the core.
Clay bricks to surround.
Fireclay
sacreet brand #100 sacks of commercial builders sand.
And more...