Right Rear Corner Box Purpose????

BGTV8

Step 1. Type "evap canister" into Google
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EVAP canister:

The EVAP canister houses 1-2 pounds of activated charcoal that acts like a sponge by absorbing and storing fuel vapors until the purge valve opens and allows the vacuum of the engine intake to siphon the fuel vapors from the charcoal into the engine intake manifold.