Cob coper tub is it doable?

Hi all,
I am new to this forum, so excuse me if this question is not in the right place. I am excitedly planing a cob house. I am planing on building a outdoor cob bench with pocket rocket, to work out all potential problems before I begin. I have lived without running water before, and without hot water ( now) and I don't want to do it ever again. Being deprived of a good soak in a tub, has left me designing variations of affordable tubs that can work in a cob house. I thought I figured it out but wanted to run it by those of you with experience. If I sculpted a great soaker tub out of cob, and first coated the cob with a linseed and beeswax clay slip, and then soft malleted a copper sheet on to the cob, it would be water proof. I would have to design the drain well. Does cob react with copper? Would it just be too damp of an environment for the cob? Any thoughts? suggestions?

I LOOOOOOOVE copper tubs!! However, I have to say that making one from scratch would look like a child's science fair project gone bad, at least if I tried it. I love the idea of a cob tub, but i think trying to hammer the copper to the profile of the cob would yield air gaps between the cob and copper, and trying to fit the drain after the fact sounds like trouble. What I would do would be to, A) save for one of those nice freestanding bought tubs (you can find a good selection for around $2000) or B) build a framed tub profile and tile the whole inside, and build cob around the outside.

Don't mean rain on your parade, if you have the metal smithing skill then perhaps you could do it. I'm all for doing things yourself and building things from scratch.

Air pockets! Didn't think of that. I suppose wet sand base is not feasible over cob. my son is a Blacksmith/swordsmith, and thinks its possibly doable. I was hoping the maliability of copper would avoid air pocket type problems... I will make a small sink bowl complete with drain to test it out. Will report back!
I just now realized I left a "p" out of the title for this post, spelling is not my strength.

Build the tub first and then cob around it.

How about sculpting the cob tub and lining it with something like Fero-cement? I don't know how you feel about cement but if done properly a very thin cement lining 1" or less with a cement slip finish would be fairly smooth and waterproof.

Ray

Well, I have nothing aginst using small amounts of cement where needed. The lime it leaches is good for the slightly acid soil that we have in central southern tier NY. I think that even polished cement will leach lime, and being 50 I don't need anything else besides weather and age contributing to the break down of my skins elasticity. I think that woul be a great idea for sinks and showers though. I am stubbornly attached to the copper tub idea. I'm going to try a small scale model. I haven't even tested my soil yet, so this is still in the theoretical stage.. I may Chang my tune when I start digging. Would the tub need a foundation under it, do you think? I was planning on running the last part of the rocket exaust under it for a warm tub ( vurses a hot tub ) effect.
As far as making the tub before hand, I understand that that makes practical sense. I think I am in love with the idea of sculpting it out of cob, and have no idea how to create supports for the copper to mould a tub I would be happy with, and no idea how it keep the structural integrity of it while moving it to transfer into the cob. (wow, that's what I call a run on sentence)...