I'm finishing up my design on a RF build using a 28" x 82" propane tank. My firebox will be on the end of the cook chamber. I'm planning on designing the firebox so that the wood sits on a grate that's 4" above the bottom of the firebox which will allow the ashes to fall into a removable ashbox. Also my air vents will be below this grate. So, do I use the dimensions of the entire firebox or just of the area above the grate? If that doesn't make sense I'll throw some numbers out there to really make it confusing... The calculator says my firebox will be 28"wide x 24" deep x 24" tall, should I use that or make it 28" tall? Thanks!