The SHO Shop heatshield doesn't look like much but does a good job of sealing the area between the battery and strut tower. If you do a homebrew heatshield that doesn't seal off this area, a hose ducting below to the front of the car would be required. The mailbox idea sounds interesting and should holdup to the heat since they are designed for longterm exposure to fairly high heat. Judging by what I have accidently done to tupperware in the microwave, I have my doubts to how well tupperware pieces would holdup to the heat on a longterm basis.
