I am persuaded of the merits of mounting SSRs on the back of a heatsink that sticks out from the top of the control panel, as in Kal's build. Some of the heatsinks I have seen look excessively large though.
My panel will be a BrewTroller type thing with a 12V power supply inside, which lends itself well to forced convection by means of a little PC fan or two.
Presumably I could get away with a considerably smaller and cheaper heatsink this way. For example, the 'medium' heatsink from ebrewsupply (12" long, $38) corresponds approximately to 300mm of this heatsink from ABL:
Take a look at the graph on this website. Under natural convection, its thermal resistance is 0.5°C/W. Under forced air (i.e. with an appropriate fan), you could get the same cooling with a heatsink just 75mm (3") long.
Has anyone done any calculations of this sort?