I'm looking for a stealth type sub enclosure for a 2002 ford explorer?

I'm trying to find a custom enclosure for a 2002 ford explorer that would fit in the rear side panel or some other crafty spot and not take up trunk space. The only one I can find that says it fits an 02 non sport trac explorer is the jl stealthbox and its $800. Not tryna spend that much. Also open to building one myself but I've never dabbled in the field and would need some pretty detailed instructions. Thanks