Some quick background information: working on PCB in an enclosure to make sure it doesn't overheat or to prevent it from doing so by adding heatsinks or some other solution. 
1) Used materials with similar thermal conductvities (because I cannot make my own material properties) but sometimes very different properties otherwise.  Will this affect the simulation in a way that would impact the results I care about enough to significantly skew them? (heat distribution and maximum temperature)
2) In Solidworks 2011, I believe you have to create an enclosure around the object to account for the air around the object (because one test simulation ended up with multithousand celsius values). Is it the same in 2013?