 
 1. How wide to build it? 16" uses 4x8 the most efficiently. It is a mid sized suv, smaller than a suburban but larger than a rav 4.
As far as installing I'm using a 300 watt v2 monoblock amp which has no highpass. 2. What could I do as far as a passive highpass? Budget for that is around 10$. I'm not afraid to solder up my own.
3. What about limiting? I know it's car audio and your not supposed to but do they make a resistor that limits voltage? Not looking for a ratio resistor like for leds.
4.Also how do you hide power wires?
My plan is for her to not have a clue until she starts her car
 she has a radio put in it so hopefully it will have RCA sub out. I will be building at my grandmas again, love it there better than my garage cause My dad and bro have their projects going.
 she has a radio put in it so hopefully it will have RCA sub out. I will be building at my grandmas again, love it there better than my garage cause My dad and bro have their projects going.

 . but the plexiglass is cut and drilled! I used 1/4'' acrylic stuff and it was 20$ for a 12x18 piece at fleet farm. I was worried about it spiderwebbing, but it didn't. I used a circular saw and had the blade as deep as it would go to prevent chipping. there never was a hint of cracking or chipping, maybe I was just paranoid.
 . but the plexiglass is cut and drilled! I used 1/4'' acrylic stuff and it was 20$ for a 12x18 piece at fleet farm. I was worried about it spiderwebbing, but it didn't. I used a circular saw and had the blade as deep as it would go to prevent chipping. there never was a hint of cracking or chipping, maybe I was just paranoid. 

