Hi Joel; Welcome back!
Well there is no hope for you now!
You have contracted the deadly RMH virus.
The only cure is to build your own RMH AND after that, to keep it in remission , you must tell any and all strangers all about rmh's and how super awesome they are!
Congratulation's ! You are taking the first steps to becoming a full fledged rocket scientist! Continue to wear your jeans and tee shirt until your lab coat arrives...
Now lets see about answering your questions.
Yes ceramic boards for the burn tunnel and split firebrick for the feed tube. I did notice some difference in ceramic boards , but not like the difference between blankets.
I carefully wrapped my burn tunnel with foil to help hold it together. Then surrounded it with clay bricks. Use no metal screws.
When I build another, I plan on making a thin plywood form to go inside the burn tunnel (will burn out with the first firing) This will keep your tunnel the correct size while building , as I found out on mine. Without a form, it is hard to keep a uniform size in your core as you stack brick around it. I had to disassemble part of mine to correct that problem.
The riser simply sits on top of the core, I did bracket it with bricks at the bottom and then stuffed C.F. blanket to seal it up.
A close look at my shop heater build post will show you how I did things.
Now about barrels. As you see, I used one on my shop stove to get the instant radiant heat. My shop is uninsulated. If this was in an insulated house I would have gone with an all brick bell instead. No need for rapid heat in a warm building.
The ceramic blanket has successfully sealed masonry and metal. A lot of folks told me it wouldn't. So it can be done if you like.
Your bell can be built with refractory mortar if you can afford it or assemble with fireclay and sand. The big difference, is clay mortar will pop free if banged to hard. Good news, is it reconstitutes with
water and you can
reuse it. Refractory mortar is forever... Oh and a #50 sack of fire clay is $7-20 a sack of refractory is $50-100... I used clay!
About the CF blanket you located on amazon. Might be fine , I don't know as it is not morgan super wool.
To start #8 is overkill, #6 blanket works great. I wouldn't think you will need 25' . I bought 12.5' and it gave me
enough for two risers and plenty of extra to use on my bell build.
It is so exciting to build your first rmh! Might I recommend building a temp core out in your
yard , just to
experience it. Really gives confidence when your doing your real indoor core!
And ... you won't have to wait for summer. If you try this be SURE to use clay to stack your core, dry stacking has many air leaks and your rocket won't blast off .
EDIT) I would aim for 45' ISA Joel, 30 just seems to small. I'll also toss out that 8" J tube is easier to work with. More room to load and longer burn times.