Poor Man's first build

For my first post I would first like to say "Hi!" from Arlington, TX. I am a senior at TCU and severely lacking in the cooker-fund department. I am an experienced smoke chef and I have been strongly considering making my first smoker. I want to go on the larger size to accommodate some of the parties I have been asked to cook for in the past. I understand that they are not real efficient, but I have been looking at the double and triple barrel designs and think that I could make some real improvements to help increase the efficiency while still keeping the price under $400.

Below are some CAD renderings of what I am looking at in terms of basic design. The firebox would be fully insulated in 1 1/4" firebrick and mortar, and all seams welded. The design is a modified triple barrel designed to resemble the "Diamond Plate Pit" style of the firebox behind the cooking chamber.

I already have a line on a trailer (likely for free) which will cut down on cost considerably, and I can get clean, non-lined, food-grade barrels around here for $15-20. I would love any comments, questions, or concerns any/all of you have.

Thank you to everyone! I can see everyone's ideas and can see how they would work better than the initial idea I drew up.

Smitty, thanks for the words of painful honesty, and for the alternative ideas. I really like the air compressor tank you found and now I'm starting to think that a moderately sized reverse flow might cost about the same if I don't add a warming box. I am a decent welder, just haven't welded in a couple years, and have a friend who is lending me his 115V MIG. I am not doing any formal catering just cooking for our very large Sunday school class at church, and that's cooking for about 40-50, and I'd like to have something to take to competitions. Also I've had stick burners and charcoal burners and I personally prefer babysitting a fire. I'll let ya'll know what I decide to go with.