I've got your install covered
first thing is first, you said you needed a cover for the front of the box.
itll be made from 1/2 inch MDF. youll cut a beauty panel that conforms to the sides of the trunk. This will have to include two slots on the sides to let the trunk arms through, as well as three cutouts for each sub plus port. here are the specifics about that:
when you do the sub cutouts, you can cut a "rough" estimate (as long as its too small!) where they are supposed to be. this will include the port. there should be an extra mm to half centimeter of wood all around that youll trim in a minute. make sure the sub cutouts are the
mounting diameter, not the overall diameter!
now attach the trim piece on the box as it will sit in the car itself. the proper location. screws will work, this is only temporary. Or, you can mockup the permanent attachment system, its all good. "grille inserts" used to hold grilles on home theater cabinets will work, or you can go with 1/4 inch dowls holding the two together, or even screws with trim caps on them to look nice. whatever you want.
Anyways, now you are going to chuck up your flush cut trim bit into your router or rotozip. itll be best if its got a 1" cutting blade. come in and set the depth so the roller rolls on the CUTOUT diameter of your box. when you lay this trim panel over your speakers, itll cover the mounting screws. all you will see is the surround sunk under the panel. sweet
next put in your 1/2 inch roundover bit, and set the depth so the edge just barely nicks the surface of your trim piece (make the roundover as deep as possible without putting a step on your trim piece). go back around your port opening and put a roundover on it. the roller should be rolling on the inside of the port, not on the trim piece. if it is, flush cut it then come back with the roundover.
you may have to pull some tricks with the edges of the port opening, but if they arent extreeme (and they wont be if your flush cut bit is a narrow diameter) then the roundover will look nice, and blockage will be at a minimum.
now reset the depth so the roller easily rolls at the bottom of the trim piece and come back through your sub cutouts, cutting a nice roundover to make the transition to the surround more gentle. if you have to flush cut it to the OD of the subwoofer, I'd skip this step, and just sand it a little bit. not much.
now you nab your matching carpet (matched to the trunk) and wrap the trim panel. tug on it hard, and you can get the carpet to wrap down the sub cutouts, all the way to the back side of the panel. you wont need much coverage on the back panel, less than an inch, if you cant get more. whats important is that the carpet rolls all the way around the nice edges you just gave your trim.
now you can install your box, loaded and totally uncovered, into the trunk. When you attach your trim panel, itll cover up the mounting screws and transition into the port VERY well! (I might come back with black spraypaint and do the inside of the port)
next comes the floor.
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now the floor. you said you wanted to let the amplifiers breathe. you are either concerned about heat totally, or not at all, so Ill make a recommendation based on heat management. if its not a concern, just pull the fans and call it a day, no problem:
I personally hate looking at wiring. hate, hate, hate. so Ill recommend you hide the d-blocks. just make them not even seen. thats my style. if you want to see them, modify my spec. I'd hide them.
so, youll have your tub made and your amplifiers mountable under there. I will assume you have the floor carpeted so if you look down through a cover at the amps and see extra, youll not be looking at messiness. Furthermore, I'll assume that you had to add some blocks to level the amplifiers, so there will be some space under the amps. Perfect place to tuck in wiring before it travels, unseen, to the D-blocks!
now, I HATE to see where the wiring pokes into amplifiers, so when I am cutting out the windows in the floor, I make my holes undersized. now I dont ever really see an amp boundary. Alternatively, I can cut a hole sized to the ID of my casing, flip the amplifier upsidedown, and bolt it to the floor. Now, when I open the trunk I see amp guts. sweet!
next, holes for fans. The idea is this:
http://www.bcae1.com/images/gifs/amprack.gif
say they are 80mm computer fans. simply cut two 80 mm holes in the floor. done! the fans will mount to the backside using standard PC fan screws (dont forget to predrill!) and the fangrills will mount to the top of the floor in the same fashion. if you want the grills just a little countersunk, buy a forstner drillbit 1/8th-1/4th larger than size of the fangrille mounting tabs, youll be able to sink it down lower.
youll have to carpet the floor before mounting either the fans or the grills
next the plexiglass covers. chuck up your 3/8ths rabbet bit into your router or rotozip and route out about 5/16ths to 3/8ths down your amplifier exposure holes. note the rounded corners, this will come into play later.
now you can carpet the whole floor. Just like the trim panel, youll be carpeting down the sides of all holes to the back. You may need a block of wood to push in the carpet into the rabbeted space. Make sure its clean, or youll mash sawdust into the carpet fibers.
now you can mount your fans and prewire them to a relay set to feed them power with REM. Dont forget that one is to be "push", and one is to be "pull" The small airspace the amp sits in actually makes the air flow faster, increasing your cooling effect
now you can buy plexiglass. If you want to do it before you carpet, go ahead, but keep in mind the carpet takes up thickness! so size accordingly (you recall we routed deeper than 1/4 inch? thtas why!). I have a local tap plastics, and they are REAL good at what they do, so i can take a shape to them and ask for a piece of 1/4 inch plexiglass cut to that shape, and they kick butt. if you have to cut it yourself, so be it, I'll expect you to know how to take care of that fully.
now you can insert the floor, stack the box on top, secure it, add the trim panel (your trunk should now look superkickass), add plexi, and take some beauty shots.
You can expect this to take longer than just this weekend. But the results will speak for themselves. Enjoy.
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you may want a grille for the subwoofers. Easiest thing using my install schema will be a custom built grille using 1/4 inch metal rod, and will have to be planned for before carpeting your trim panel. nab some metal rod from home depot or anywhere you'd like, along with a pipe bender. stainless might be the best idea.
cut as many lengths as you would like. I like to use a non standard number, its personal preference. I also like to stretch them across both subwoofers to make less work for myself. thats your choice.
I can then bend the edges using the pipe bender, then drill 1/4 inch holes at the appropriate locations around the subwoofers. I then cut out the carpet a bit to aid installation. fitting the rod is real hard, but its very secure. and thats better in this case, then having loose grill work!
alternately, you can find 12" wide drawer pulls from various hardware stores. buy four, and install them around the subwoofer locations. they will screw in from the back, so dont forget to countersink the holes back there! Less work, and might end up looking better. you might be able to do this with the trim panel ALREADY carpeted as well.
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