Hello, I am new member on site, looks pretty neat. looking forward to trying some of the recipes and hearing back from others on site. My build question is for my trailer mounted grill. It is an extremely heavy duty build! has a few round pipe outlets on sides that i'd like to use. my idea is to build a firebox underneath the grill, and connect via one of the large round inlet tubes. is there any general rule of thumb to how big, where to locate, what to include in the fire box build?? any help is appreciated.