Orrrr just setup a camera hooked up a screen in the dash or your headunit (assuming youre running one with a screen). Super super simple and very much worth it.
Every corner that gets cut in a build like this adds up very quickly to the whole setup not performing like it should.
-Running 3 21" woofers in a truck for starters isnt ideal at all because of the layout so that will certainly limit your performance.
-Trying to tune it too low IMO will hurt it quite a bit by the numbers although IF it works out it will be gnarly to the body
-Not going with a full wall, is going to limit performance hugely.
Not trying to hate...not at all. I was actually in the exact same situation when I was 17 building my first walled vehicle. I felt way too uncomfortable without a rear view so I decided to mount my woofers low (2 18s) and large port at the top of the box running horizontally all the way across just like the lifted dodge linked above. And the wall itself was contoured exactly to the rear window of the car and the wood was siliconed to the window. With this I could look out my rear view, through the port and out the back window. However this was 2002 and screens were super expensive and I was a struggling athlete trying to make a couple dollars on the side.
Definitely definitely suggest going full wall (youll ******* love it bro. Honestly...the look, the feel, and the results you get are well worth it!!) and run a good camera out the tailgate or even out the back of the cab at the top maybe. Then you simply have an easily accessible switch hooked up to your head units reverse input that you can either leave on permanently while you drive to glance at orrrrr have your regular screen controls on and if you want to switch lanes or look behind you just quickly flick the switch and have a look. But to be honest, you dont need it. Driver and passenger mirrors are all you need anyway. Its just like driving a work van/moving truck etc. No big deal, you get adjusted to it very very quickly.
