You NEED an upgraded alternator, the PC21400 wants a LOT of current (I believe it's fused at 140 amps). Any number of batteries will only delay the inevitable, as no matter how much power they store, they gotta recharge sometime!!
BUT - who is quoting you $1000 to redo the alt?!?! Mr Alternator (
www.mralternator.com) will rewind your existing unit (and powdercoat it if you like) for around $300, and their work is great, turnaround very fast. I've used them many times.
Other notes: If those subs are dual 4 ohm coils wired correctly, you have the amp bridged to 4 ohms, which is what it wants - in your description, you mention that you think it's running hot because of the 4 ohm resistance. First off - that amp runs hot anyway, A/B amps with that output usually do. Secondly, if your voltage is dropping (it is), then the regulated power supply has to draw more current to make power, which both aggrevates the problem (since lack of current output ability is causing the voltage drop in the first place) and makes the amp run hotter.
Read the "Low voltage/dimmin lights please read this!" sticky at the top of the forum, it covers this in detail!
If you want more SPL, a couple ideas:
First, turn the box around. You're getting a good bit of cancellation firing them forward like that. Secondly, a ported box is a good idea - properly tuned, this will also increase power handling. Lastly - the RFR's are pretty good, but to handle that power, there are better subs out there for both SPL and SQ.
Hope this helped!
