Self-adjusting tonneau cover assembly

A tonneau cover assembly comprising:

• a front rail;
• a first corner piece coupled to a first end of said front rail;
• a second corner piece coupled to a second end of said front rail;
• a first side rail coupled to said first corner piece;
• a second side rail coupled to said second corner piece;
• a first self-adjusting device coupled to said first side rail opposite said first corner piece, said first self-adjusting device including:
• a first stop coupled to said first side rail;
• a first spring disposed between said stop and said third corner piece;
• and
• an interconnecting plate coupled to said first stop and to said third corner piece, said interconnecting plate including a slot for accommodating sliding movement of a fastener passing through said slot and coupling said interconnecting plate and said third corner piece;
• a second self-adjusting device coupled to said second side rail opposite said second corner piece;
• a third corner piece coupled to said first self-adjusting device;
• a fourth corner piece coupled to said second self-adjusting device;
• a rear rail coupled to said third corner piece and said fourth corner piece;
• and
• a cover removably coupled to said front, first side, second side and rear rails;
• wherein said first and second self-adjusting devices automatically move said rear rail away from said first and second side rails as said cover expands with temperature increases, and automatically accommodates said rear rail moving toward said first and second side rails as said cover contracts with temperature decreases.