You want to burn the charcoal until it stops smoking outside. Move the non-smoking coals into the vehicle, either in the portable grills or move the coals into metal buckets placed on bricks so they don't melt anything and cause unnecessary fumes. 15 lb will be more than enough for a regular size car, a great big vehicle like a cargo van or something like that you'd probably want to use a bit more. Tape the air vents and obviously don't have any windows down. There's a thread about it somewhere on this forum. I wouldn't get too hung up about the particulars, 15 lb will be more than enough for most vehicles although there is I think some kind of mathematical equation for determining how many pounds you need per metric cube of space or something like that, I don't think it's really worth getting that technical, but you'll want to look at that CO method thread yourself if you have questions along those lines. It's probably one of the most peaceful, effective and under used options, and I don't really understand why...wish you well