Just my opinion, but I'd opt to leave it under the hood and use a lightweight modern battery instead.

The weight of 20-50ft of 1/0 cable certainly adds up. Also, consider the aggravation of voltage drop, high resistance grounds, hot start issues, cable routing, and the real potential for meltdown failure with 25ft of constantly hot line running under the carpet day and night.

If you do choose the trunk route, figure out your total maximum potential amperage load first. You will probably need larger capacity wire than what is provided with most cheapo kits.
ECU, injectors, fans, pumps, stereo, headlights, horn, tailights, domelight, A/C, signals, markers, brake lights, 12v acc, oxygen sensors, ect.