[TigerOats]

I don't go along with that evap size. I have been working on this for some months now and my examination of many fridges with freezers shows the evaporator being 4-5 times the size of the condenser.
A/C units could be used but then you must go along with the freezer concept of a much bigger evaporator to get sub-0 temps. A/C units generally only cool to the 5-10C range.
The use of propane is a good choice. You will find an excellent link to converting to propane in the Project-X thread.
The use of a small condenser and a waterblock as a evaporator will probably lead you into the minefield of good temps but insufficient refrigerant mass to effect cooling. If you think about it this way - if because of space you decided that you would use a micro pump instead of a normal pump. The water would be flowing but there would not be enough flow to cool the system. The same applies in this instance - you'll get the right temps and pressures but because the refrigerant is boiling off too quickly you won't get the result you want.