my diy chiller is actually an old vapochill classic. it's a phase change cpu cooler designed for subzero tempts for maximum overclocking. based on it's age it doesn't keep up well with moder cpu wattage so i slaped a water block onto the cooling head and run a pump to the pond in the summer time. works pretty well and drops the pond a few degrees. Would probabally do much better on an aquarium.
in the computer overclocking world many have tried to pair watercooling with the college mini fridge. most systems fail as the mini fridge was never desingd to handle a continuouse heat load like that generated form high wattage components like video cards and cpu's. Thus the compressor on the fridge gives out and any unsupervised machines fail. (ie they left it folding and went somewhere).
in an aquarium where the heat load is not so high it may work, but I'd definetly setup several fail safes if the fridge dies and test it for a while before adding any fish to the setup.
remember the first fail safe is maiking sure the pump and the fridge are hooked to a switch so that both go on or off at the same time. if the pump is off, the fridge will freeze the water lines. google search mini fridge and watercooling to get some ideas and remember most of the guys setting up those systems don't have to worry about living creatures.
Pretty much.
step one: turn the fridge so the door is facing up (this is now its permanent position)
step two: drill and seal your in and out fittings.
step three: pick pump and place.
DONE.
so no, you are not far off.
A 50 litre 12 volt car fridge used as a sump or a fridge with a sump inside with the pipes through the side would work if it was set to the correct temp