Building a portable 12v system

If you want the low notes (and battery power is really going to dictate this) then why not build a large reflex sub housing all 4 drivers? You could still run 2ohms and it will go much lower then the other two.

I would at the very least build just 1x MTH30 1st to see if you like the sound and if it plays low enough for your liking as because your making it portable to make sure you don't drain the battery bank fast you would need a fairly high (sub bass wise) crossover point.

Remember the 1/8th rule of "music power" - when playing real music, your long term average continuous power is about 12.5% of whatever the instantaneous peak power is. EG if you calculate that your amp would draw 20 amps during peaks of full power into the drivers you have, then over the long term it will be drawing about 2.5 amps, and you can use that figure to estimate potential battery life. This rule is less accurate if your music includes a lot of continuous sub-bass tones, or is scored for only triangle and piccolo.

Don't forget a good multi-way fuse box/distribution board. Every significant length of cable needs a fuse in it close to the source of power, even if the destination device is also fused - because in the event of damage to the insulation leading to a short circuit, both lithium and lead-acid batteries can *easily* deliver enough current to start a fire.

The answer is, not much fun...it'd be a three person job. My bike trailers are ~60kg with everything on, and they are a challenge to move up any kind of hill by yourself, even with the mechanical advantage of bike gears.

I used P.Audio SN6-150CX 6" coaxial drivers in my mid-tops, with a custom crossover, which took a long time to make. But if I was going to build again, I would probably go for an array of Faital 3FE full-range drivers; they would be a lot lighter, even if you used enough of them to match the output of the P.Audio driver, and need no crossover.