Hello. I just found this site and wow you guys are all cool pyros!
I've been building and using rocket stoves for about 10 years now, taught directly by Ianto at a couple of his classes in Cob Cottage (you should go if you can... amazing). I have a 15-gallon "pocket rocket" that heats an upstairs room that has been cleaned only once in 5 years. I cook it hard since it has a cob wrapper on about 3/4 of it's surface. The interior is fine. The barrel has no bottom, instead it sits on two fire bricks, which site on cob which sits on "insulation cob". I have a metal cutout that sits on top of the two fire bricks as the bottom, which can be replaced (but hasn't been yet).
The feed tube gets replaced about once a year because it takes a beating. My exhaust pipe is still going strong - no signs of wear-through yet. The previous poster gave critical advice. Burn the hell out of your bucket before you take it indoors. I make a fire on my side walk and roast the inside and outside of the barrel which removes everything and also imparts a nice metallic black finish. Cook the lid too.
I am building a sauna now and plan to use a 5-gallon pocket rocket with 6-inch feed tube and 3-inch exhaust pipe. That about takes up the available space on your lid. I'll put the stove on top of a pad of insulate cob with dry rocks stacked up around it. If the rocks seem too bulky, trust me, you will want them. Your bucket will glow and you want the rocks to absorb the radiated heat or it will fry the wall.
I have two rocket stoves inside my house, which is a conventional stick frame house. I install 2x2" wood over my sheetrock on top of studs. Place tile-backing fiber board over that to cover the entire space along the wall that will touch the cob. Fill the spaces with perlite from the open edge at the top then cap it off with another 2x2" board running horizontal (to the finish height of your bench/stove). This will keep your house from burning down. But you need more than that for the stove area. Use insulation cob made with clay slip and sawdust or whatever. See Ianto's book for ideas. I have a shop and lots of sawdust so that is my preference.
More hints: after getting my thumb sewn up, I always fold back the rim of the feed tube about a quarter inch to make a nice smooth edge. Cut ducting pipe is super sharp and you reaching down there a lot. I tried aluminum tape once but it just burns off the sticky and then falls off. Burn the bucket and lid in an open fire outside until it's a gorgeous metallic black. Your lungs will love you.