No worries been there done that.
My first box i made was plexi glass. For my 91 s-15 gmc single cab lol. Put 8 8's in there and ended up sounding like i had 10's in there. Wouldnt recomend going with plexi glass only because its a pain the ass to work with.
I agree with what atreyu is trying to say and ive seen friends and people do what he is arguing about. Hell ive even done that back in the day before i knew anything. Hence why my first box was plexi glass lol.
When i get the truck i eventualy want i will be going with single sub for more power due to room avaible and not going remove my back seat like douchebags ive seen do.
Btw theres plenty of websites that sells complete boxes for dirt cheap made out of mdf 3/4. And no im not talking about crutchfeild that website is a joke and super over priced.