UPDATE #3:
IT'S FINISHED!!!
Only bummer? that I was hunched over for so long that my back is sore.
Here's the updated schematic:
Now when the box receives 120vac, the 25/30A Switching Power will supply power to the rig. At the same time, the battery tender will charge the battery.
When I lose 120vac, the DPDT will disengage and automatically switch over to the battery... My rig will still continue to run without interruption.
Here's the innerds:
and here is the overall look... also with room for 120v power cord, 12v splitter, and/or anything else I want to add.
Bottom two fans sucks outside air in, top two fans suck hot air from the inside out. They only operate when the 120vac is plugged in.
ETA: It is a very tight fit and with a little bit of velcro in the rear of the can, it's not coming out without some force.
Now I've been asked... why not just hook up a battery directly to your rig OR just the power supply itself? Well yeah, I could do that... but why not both (ARFCOM's answer to everything). And both are in the ammo can, sans the battery. That's is another project that I will be working on.
So, my next projects are:
Ammo Can Battery (similar to Piccolo's setup)
Ammo Can Digital (netbook or small laptop, external sound card, etc)
Ammo Can HF (HF antenna with cables, small auto tuner, connectors, etc)
Ammo Can Tool Box Kit (Essentials for ham radio: soldering iron, screwdrivers, parts, etc)
Ammo Can Food (Gotta Eat)