if those rears are anything like the 4th gen camaro i have, you need to pull the whole panel to access them. lots of people put midbass there with good results. depends how deep a speaker that will allow for though.
i plan on just a 10" sub. nothing crazy. just added to the factory system will be fine. thats how im running my camaro with the factory "monsoon audio" upgrade plus an infinity powered 10".
this setup is a TON better than the original AE86! haha 4" dash speakers pointed at your shins, and 4" rears pointed at the roof. THAT needed an upgrade! this should sound just fine. my wife's '11 altima sounds great and its just the 2.4S with normal audio. "new" speakers usually sound fine these days. at least for the upper half of the spectrum.
however im getting worried about rear leg room. my kids seats will BARELY fit, and they would have to sit indian-style! and speaking of, those are definitely child seat anchors at the rear deck. they pop up like they did on my GS300.
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Sold my 94 S14 for a 1998 Z28 Camaro. Woops.
Springs, Shocks, Sways, Bushings
Cam, Lid, magnaflow catback, BBK intake manifold, LS7 lifters, ECU tune. good for 400 hp.
sure its fast, but it drifts like a boat.