my i3 8x8x8" with a standard heatbed (12A power supply) seem to not have problem with "overheat"

http://www.dx.com/p/stc-1000-1-7-lcd-mi … 20v-259160

to control fans.. (thats what i use in my own heat chamber)

you can hack it to use 12v instead of 220v for the powe supply (easy hack :  http://www.digitalspirit.org/blog/index … e-STC-1000  sorry, it's in french but you will understand with the photo.. there is only one component (a 220v to 12v transformer) to remove as the controller already work with only 12v)

you can found 110v version on ebay or amazon if you don't want to hack it..

this controller can control a heat source and a cool source... (i only use it to cool down when i reach the max temp of my enclosure)

I personally went with the stuff from home depot because it was cheap had a decent operating temperature and was easily acquired 
since I live down the street from home depot.

The interior chamber heater is great for start-up, but offers little benefit once printing has started.

The extrusion nozzle and the bed heater dump lots of heat into the enclosure, reducing the amount of additional chamber heat to zero, when the printer is running.

Not necessarily true
keeping the enclosure heated to a minimum of 55°C provides greater layer adhesion.

My printer is fully enclosed and has insulation and I was able to only achieve an ambient temperature of
37°C with the heated bed and the extruder.

My prints were much more reliable and stronger when printed at 55°C

The extrusion nozzle and the bed heater dump lots of heat into the enclosure, reducing the amount of additional chamber heat to zero, when the printer is running.

Our SD is enclosed with a cardboard box and heated via a personal space heater pointed through a hole in the side of the box. Interior temp hits 50C (this is read via the temp reading from the extruder before the extruder is heated). We also use a glass bed and hairspray. No lifting from the bed.

Does this work well for you? With out a simple box. I get cracking in my prints that are over 4 hrs.

So 70C is where ABS no longer shrinks/warps?  I thought it was higher then that for some reason..

90C is the transition line, but is gets quite soft from 80c-90c. At 70c is does try to warp, but very quickly the stresses in the material creep and fade. This I believe is why 70C is a great temp point. Any higher and parts are stiff enough while printing, and lower it doesn't fade stresses quickly enough.

The 50c you want to do is a little low.

What's the point if your not going to hit the temp where ABS tends to stop warping?