How I did it
For the benefit of those who might try this simple installation in the future, here's a synopsis of how I went about doing it.
1. Solder a 10 GA ground wire to the existing ground ring terminal on the Painless fuseblock.
2. Open the end cap on the passenger-side of the dash. Drill a hole at a convenient location in the metal framework of the dash support large enough to accept a bolt and locknut. This is to secure the ground wire.
3. Slip the Painless fuseblock into the space in the dash, allowing it to fit snugly down in the bottom. Don't worry, it won't move around in there.
4. Snake the wiring down along the structural support just underneath the glove box lower hinge. Use wire ties as necessary.
5. For the pink +12v signal to the Painless fuseblock relay, I spliced into pin 1 of connector C1 behind the heater control panel. Connector C1 is the smaller of the 2 connectors that plug into the heat/AC control panel. Pin 1 is the top-leftmost pin when you're looking face-on at the pigtail with the clip pointed up. The wire is blue.
6. Route the 10 GA red battery wire through the firewall (I used the empty rubber plug under the clutch pedal).
7. Bolt the circuit breaker to a convenient location near the battery. I attached it to the plastic battery tray. The Painless instructions suggest using the firewall or fender panel.
8. Clip the red power wire, attach a ring terminal, and screw it to the "AUX" side of the breaker. Use the leftover wire with a ring terminal on each end to attach the "BAT" side of the breaker to the battery (+) post.
I "enhanced" the Painless kit by using watertight shrink-terminals and butt connectors at all locations except the (+) battery post connection. I have experienced no problems with this installation.