whats a good size for the firebox
Should I go ahead a put it on a trailer in case I might want to move it
how small do you wanna cut your wood seems an important part of that question. Also I second the wheels, if nothing else just to move it around the yard. If you don't plan to actually tow it with your truck, I'd suggest at least 4 big wheels. mine has 2 dinky wheels and the shelf below it keeps whacking my shins as I move it.
I have built several grill/smokers almost like your design. The difference I see is that on mine, I had no seperate fire box. I used the grill section as my fire box also. I had one exhaust on the grill section and one exhaust on the smoker section. I opened the exhaust in the grill section if I wanted to use the grill or opened the exhaust in the smoker section if I wanted to use the smoker. I also had wheels on all of mine to be able to move them. As far as the size of the fire box, look here and see what you need. Lots of good information here........
I want to thank everyone who responded. I think a trailer is the way to go. There will be about 2 1/2 4x8 sheets of 1/4" plate.
The links for the calcs is great.
The side firebox is not set in stone, but maybe it should be in the middle? Might allow for better control of the heat into both chambers.
Not pretty but maybe more functional.