Google: ford ranger subwoofer enclosure image
To get some ideas
You don't want the subs facing each other unless you run them in opposites phases(reverse +/- on one of them)
"like frequencies cancel each other out"
This means you will get "flat spots" when the same frequency waves meet.
Subs are there to generate low frequencies, these are long sound waves so travel longer distances, this is why you can hear the thump, thump of a sub from 5 cars back at a stop light but can't hear the song, lol.
So 2 subs in a Ranger cab is a bit much, but to each his own.
Because subs need to generate longer waves they need a larger box, you can add batting inside sub enclosure to "mimic" larger box size.
Wattage, this confuses most people.
Is 2 watts twice as loud as 1 watt?
no
10 watts is twice as loud as 1 watt, it is a 10:1 ratio
If you have a 100watt amp, and change to a 200watt amp you will get a 10% increase in volume, so it wouldn't even be noticeable to human ear.
If you have a 250watt amp you would need to go to a 2,500watt amp to get twice as loud.
So save your money, wattage numbers can be deceiving.
When someone brags about a 2,000watt system, say "oh, so twice as loud as a 200watt system"
Speakers will have a wattage rating, Continuous Power Handling, and possible Peak Power Handling
If Continuous is 100watts then amp should be 2.5 X 100 = 250watts, as long as 250watts doesn't exceed its Peak Limit.
There is also impedance of speaker and amp to consider
0 ohms is a dead short and will burn out an amplifier
Speakers come in 4ohm and 8ohm
Amps come in 4ohm and 8ohm
Some amps are rated for 4 and 8 ohms and will have 250watts at 4ohms and 125watts at 8ohms listed.
As the ohms go up the wattage goes down, but as the ohms go down the danger goes up, lol.
A 4ohm subwoofer at 50% volume can drop to below 2ohms at the amp on a heavy bass note, so close to a dead short.
So if you have 4ohm speaker then make sure the amp is rated for 4ohms.
If you connect two 4ohm speakers to one channel on a 4ohm amp that amp will not see 4 ohms it will see 2 ohms, and the first heavy bass note will send it to 0ohms and a dead short, bye bye amp or hopefully it's output is fused and blows the fuse.