I am using a 275 gallon oil tank to make an evaporator. It will be upright and was wondering about the size of the firebox. I was thinking of 24 or so inches in size and then block off the back of the drum to maximize heat from the wood. Also, was thinking of making grate system on top of the evap. out of angle iron and simply placing my pans-restaurant chafing style pans, in the holders. The heat will directly be on the bottom of the pans so will heat faster. Any thoughts? Thanks, Kevin