Questions about building a small marine stove for my boat

[jdham137]

I'm building a small wood/charcoal burning heating stove for my sailboat, a 27 footer. I'm modeling the design on this stove, the Griffon;

http://www.glastonburyburners.co.uk/products.html

I'm building it out of 1/4 inch steel and the interior dimensions are 10" wide, 11" deep, and 10" tall. Here's my progress so far:

http://imgur.com/Fv5DOve

I think I might have overbuilt it with the 1/4" plate but it was a cheap cutoff at the metals shop and was cheaper than the 3/8" plate. I plan on putting a small window on the door and a vent below it, like the Griffon stove. The flue will be 4" in diameter.

I'm confused as the the liner material for this. The primary purpose for the stove is for cabin heat so if I line the interior with firebricks, won't they keep a lot of the heat from heating the boat and just send it up the flue? However, if I use soapstone for the interior, would it hold a slowly radiate the heat as it's advertised to do? Another possibility is pumice stone. I don't know what the final weight will be but I might need to conserve weight and pumice might help with that.

Any ideas or advice would be greatly appreciated.

John