Pelican Case and Heat Issue

Took a Pelican i1015 case designed for the iphone and 'adapted' it in order to use a GPS app on my motorcycle. After a short test ride, I noticed the iphone was very warm. Obviously this is due to the design of the 'water resistant' case. I suppose my question would be something on the order of "how warm is too warm?" I there an acceptable level of heat generated by the iphone in an enclosed case such as the i1015? Anybody else had any issues with this particular case?