Seems like extruded polystyrere is the preferred (afordable) insulating
material for marine icebox / 'fridge / freezer applications. [The above
conclusion was heavily influenced by Glacier Bay's insultation test,
viewable here]:

http://www.glacierbay.com/Instresult.asp

Commerically, this means either Dow 'blueboard' Square Edge, or Owens
Corning pink 'Foamular', both of which come in 1" - 3", 4 X 8 foot
sheets. Since I'm begining my 'fridge box construction, I've been
hunting for either of these products - in small quantities (like 4 - 5
sheets) with no luck. There do not appear to be any on-line retailers
of this stuff, and I've had equally poor luck finding a retailer in the
Los Angeles area.

Any ideas?

Thanks

Mike Worrall
Los Angeles