Obvious - no, annoying -yes. I run into this alot - try filtering solid bodies only in the filter toolbar and select the body in the graphics window. The whole body should select for the Sim input dialog box. It sounds like you've already tried the feature manager tree approach but if you can just locate the solid body (not the feature) that should work also.
They really should make applying temperature to an entire part/body easier. It's not that uncommon - it should be a primary filter. </rant>
Thank you, that did the trick!!
Time for my rant: I agree with you, this is not an uncommon boundary condition. I lost half a day looking for something that would logically be in the Temperature type selection box.