What's your budget for the subs?Money is my biggest issue currently, And I'm not to sure about 18's. I'd like to stay in the 12/15 area honestly.
And you have to take out port displacement(and bracing) as well in order to calculate tuning...the subs won't displace that much air space either, ~.2ft^3 each depending on the sub.That would be about 7.78cu/ft using 3/4 mdf. Kinda tight for 2-15's IMO but it'll work. You then subtract the subs displacement and Voila. lets say your subs displace .5cu/ft each that would take it down to 6.78cu/ft.
It's a '95. I could get more room If I'd do a wall, but still want to have use of the rear view. Granted that would solve my problem of my sliding rear glass being a trash can lid! And the 16" depth I am sort of stuck with since I am on the taller side and moving it up more then that I would be a bit crammed.You must have a newer S10, huh? Because I have a '92 and have way more room than that. I didnt' realize there was such a difference in body styles.