i just wanted to know if the speakers and subs will sound worse if they are mounted on a wood wall built behind the seats rather than if they were just put in boxes and placed on the floor behind the seats. and if any body can give me any pointers on building that wall to mount them on, it would really help me.
-thank you

depends on what kinda subs you have.... some are "free air" and others are enclosure....... you may have to build a box on the back of that wall to enclose the sub....

Even if they are free air, you should still build a box for them and then put an opening in the box for more sound. If you go to the search, subs and sub boxes have been brought up several times and I remember seeing a post or 2 on subs / boxes., but to just slap a sub on a piece of wood, AIN"T GONNA WORK :)

You can build what is called a 5 sided box, you will have to seal it completely on EVERY seam inside.I would suggest using spray in acoustic deadening spray. deadbeat, or dynamat works excellent! I would suggest using a sealed enclosure, a ported one is not as simple as just "cutting out a hole" to get the optimum sound response( for the frequency of the subs you use)you would need a plotting program for the computer to get the size,length,width of the port. I would say you should stay clear of that idea. thats where a good stereo shop is nessessary. I'm sure someone in here would debate this with me, and all i can say is to read the loudspeaker cookbook, and get back to me. hehe. the 5 sided box is simple, just make top,bottom,sides for it. use cardboard to make the templates for the pieces, and cut it out. use 3/4" mdf.you will screw down, and seal the outsides of it first, them screw down the face.make sure to carpet it nice......just for looks and all. the sub will have a VAS number, or airspace. usually like 1/2 to 2 cubic ft. for 10's and some 12's. look for the ones that use a reasonably low airspace.The box will need a separation for two subs. Just seal it well! this step will make or break your sound.I wish I knew how to inport pics here, I have a great shot of a 67' with a sub setup with separates on the upper side of the box, and the amps in the middle of the box. Looks super clean!If the subs have low airspace needs, this is easy. the stuff this car used is MTX amps and subs. I wish you luck, and make it your own! :)

OOPS, Its a 6 sided box for two subs! 8O

Check out my El Camino..

My El Camino (http://www.sounddomain.com/member_pages/view_page.pl?page_id=195122&make_type_query=)

I simply used a sheet of plywood to create a wall to mount the speakers on so that magnets hung free air in the smugglers box. Now I made sure to seal the smugglers box first. It isn't going to give you earth shaking bass, but then again, I wanted to hear the engine outside and the bass inside, so it worked out perfect for me. I do plan on completley enclosing the area sometime, but running on a strict budget and since it was my daily driver at the time, that was the best solution. It works great for me and it could work for you too.

where did you put your spare tire since you covered the storage area with the wall.

I made a mounting bracket out of diamond plate steel, 1/2" steel rod, and some chain. I then mounted it in the back of the bed closest to the cab. I was able to drill two of the mounting holes down into the smugglers box, which were then sealed, and two more just in front of where the smugglers box ends.

how does this sound...400watt alpine amp with 2 JL Audio 10'' subs?

I don't really know what to tell you. It all depends on personal tastes. I think that JL subs are some of the best out there, and I have heard a lot of good things about Alpine, you may want to up the wattage on the amp, I know I would. Otherwise, it is really limited to the money you can throw into it and the sound you want to produce. But for starting new, I think that combination would probably be fine.