From living in snow country before we were told NEVER use the e-brake when it is extremely cold as freezing water can bind up the park brake and not allow it to release completely. You can tell when it gets that cold by whether your outer door handles are icing up or freezing themselves when you try and open the doors.
Also - my thought on parking on a mound at an angle is that the engine oil is moved to a different position than the the engine is designed to operate under (level) with the colder temperatures and longer to get the oil to move after start up you could be causing some premature wear in the upper engine/cylinder area.

Of course if the mound semi softens you might also get high centered on the belly pans trying to get back off the mounds.

Just my 2 cents worth....... <img src="/forums/images/graemlins/pfft.gif" alt="" />