Firstly, thanks so much for your really informative replies, you've really given me lots to think about and consider. Unfortunately I can't send any photos today as I have no camera but the issues you have raised I will try to cover so you get a better picture of what I am dealing with over here.
The stage is very strong structurally so the weight of both stove and bench will not be a problem. Your description of it looking like an aircraft hanger is very much the case, it's approximately 80 feet tall and 200 feet square, completely covered but with clear open space between roof and walls allowing the breeze to blow through but keep the rain out. Due to this amount of permanent ventilation I think it virtually impossible to heat the air space so I was thinking that the bench's primary function in this would be as a 'butt warming little kitten'.
The amount of ventilation in the tent should hopefully help with getting the exhaust out of the tent as there is plenty of room above to let it dissapate. I was hoping to have the chimney visable and open vertically so the visitors could see the lack of smoke. Would a 10 feet vertical stack be sufficient?
I like Ernie's idea of a smaller wider bench with 3 passes and a 6'' system built within a frame and filled with perlite and clay. Is there a reason for the 3 passes? I was thinking of doing maybe 2 passes, like a big U-shape and have the chimney return close to the stove. Also what ratio of clay to perlite would you use?
Another question, could I use the instructions in Ianto's book for an 8'' system but with a 6'' tube or would this overload it?
Also what temperatures could i expect within both the stove and also the bench? My Health and Safety people will be very interested in this?
Unfortunately my budget for this does not quite stretch to flying you guys over here to help with this, but you would be made very welcome guests should you ever find yourselves this way. I love the Santa hat tipi idea, I'll suggest it for next year.
Once again thank you so much for your speedy and knowledgable replies, this is a great site.
Cheers all, Nathan
There is a space of just under 30 feet between my proposed bench and the ice rink so heat transfer should not be a problem, there is also drainage in between.