Well, I redid the entire audio system as well as adding a 5.1 theater video system. I took my time and sometimes took months off, but I would say it was about a year in the making. A lot of the time was in planning the system out and then building all the different pieces so they would all fit together perfectly. Taking apart all the different panels, doors, seats and dash panels several times, as well as applying "deadening material", constructing speaker door plates, running major cables and wires, etc. ... it just takes a lot of time and patience. I tried not to drill any holes to secure any new panels that I built, there were a lot of 10mm existing holes to use that I secured my paneling and stereo equipment with.
As for the cooling of the amplifiers, there's no problem, in fact, I can view the temperature of the amplifier and the voltage that it's running at from the indash Alpine IVA-D310 headunit.
As for doing the job in one day... no way! Take your time and plan things out... and do a good job.
If you'd like to see more pics, I have the RX330 on Sound Domain. I have just a few of the build pics there, as well as changing out all of the lights to "white" LEDs. Here's the link:
http://www.cardomain.com/ride/2413004