I am definitely going to do that, same constraint, need more round2its...

Wondered about the venting, because I know there are some design issues there, just not sure about the details, haven't been into the car stereo install stuff for quite a few years now.

 

I had looked at AM sub boxes . Poor quality and alot of $$. Besides, I needed "some" storage under the back seat.
My sub/ amp I had got years ago from a buddy. (still got enough components left over to duplicate )All new in box. So I built around them. Only costs' were 4'x8' particleboard (was figuring lots of mistakes and easy to work with), wire, circut breaker, converter box, felt. All about $75.00.
As far as not being in it for awhile, neither had I. "But" w/ exception to the technology, it hasn't changed much. If you are after boom-boom, this doesn't apply. If you want great, full, complete sound w/ enough bass to rattle your and enough volume to make your ears bleed as well as a clean look, something to this effect will make you VERY happy.
Ported or sealed sub enclosure will depend on your sub selection. I went w/ a 12" sealed, simply because that is what I had. A 10" would work awesome as well. IMO an 8" would be to small. Watch your available mounting depth as well when making your selection. You can fiberglass the bottom of the enclosure to make it hit harder as well as use a harder wood to make the enclosure.
That "was" my plan, "but" I was VERY happy w/ the results I got with what I used, why change . The hardest part of making the enclosure was the "sides" as the surface of the storage areas is not flat. Lots of patience and cutting and fitting . I finished off w/ 1 layer off high density foam weather stripping and evenly/ securely fasten it.
Amp: This is one thing that hasn't changed much. ALWAYS buy/ use more than the speaker (s) require. (I had to turn the gain down to about the 1/4 mark as well as turn the bass way down on the head unit) To small will destroy the speaker(s) over time as well as not sound "right". Buy as much QUALITY as you can. Again, I used what I had. Also, at least w/ my amp, I ended up running a switched acc power for the remote power on. Mine didn't like the multiple times it was signaled to turn on/ off during starting my truck. An added plus doing it that way, you don't always have to run w/ the amp (like when listening to "news" channels)
Layout: LAYOUT, LAYOUT, LAYOUT. That is everything to ensure a clean, well working final result. I had the interior (w/ exception of headliner) from the pillars back, completely out. To locate "accessible" rear speaker leads, for the converter box, I ended up using a volt meter and process of elimination (looking for "low" voltage). Main feed wire for the amp, I used 8 ga w/ circuit breaker just off the L battery. My amp was fused as well.
Me and my son spent basically a working week (this was our annual father/ son project ) to design/ build/ install. No fancy wood working tools just my basic Ryobi rechargeable's and Depot buckets for a work bench

 

Sounds good, thanks for the tips!

 

Welcome. Looking at your pics..WOW....Nice work, great pic's. I see we have same taste in blue..

 

My first of many custom pieces for my truck. These are the brackets I made to mount my United Pacific train horn, compressor, and tank.

 

well here it goes, i'll try and compare to the other good work posted on here. this is the front i did for my 03 cummins.

 

this is the current bumper i've got on my 97 cummins that i built

 

here's the rear i've built for my 97 cummins. i really like having the lights built in, it makes loading a trailer at night a lot easier.

 

the roll pan is on my 03 and the black one is another 97 that i did

 

this is the front for a buddies 07.5 duramax that i did. it's got the fog light tubes, air duct for extra air to the tranny cooler, and a reese hitch with plenty of reinforcement to it to be able to be used as a tow point or to mount a winch in.