Denzil Crews wrote: [...] the metal is approx 5/16th. I would think at the beginning of a burn cycle it would help cool downward gas faster, but retain more more heat later in the process. has anyone used heavyer outer skins and were there any changes or allowances needed because of the thicker metal.
I don't know
the answer, but you're asking a very appropriate question. As far as I understand, the barrel or whatever-you-use-in-place-of-it is meant to be a 'heat-exchanger.' It helps to cool and shrink the hot gases and get them moving down and out of the system.
I've read posts by people who want to put
cob all over the outside of their heat-exchange barrel. As far as I know, that is a very bad idea. However, the difference you're talking about (thin barrel-metal to 5/16th tank metal) does not seem as drastic as somebody putting cob all over their barrel-- so I don't know, you're tank may be fine; The difference may be negligible. Please do continue to look into it though; sounds like you're on the right track.
Another thing, you may already know: BE VERY CAREFUL CUTTING OLD PROPANE/GAS TANKS. ANY SMALL AMOUNT OF GAS LEFT IN THE TANK CAN MAKE THE PROCESS VERY DANGEROUS. There are processes for making sure its safe. There's a lot of information about such things all over the internet.