Love the creativity and the pie looks great.
It does look like oven balance is an important factor to successful pie-eating. To secure the weber to the chiminea, you might consider baling wire around the neck of the chiminea (twist tight) and wire or strap up to the base of the weber, secured with a through-bolt. Once that is in place, the base becomes more interesting as that isn't secure either. My (unconventional) recomendation for the base is dig a bit of a hole, pour in a bag or two of concrete, wrap the chiminea with thin plastic wrap and drop it in until the concrete sets. If done right, the chiminea should be removeable but offer a tight fit.