4th Edition DF chart - Opportunity Fire question

[Schoenwulf]

Had occasion to pause today as I read this thread again. In Section 1.2 of the 4th Edition Rules, the definition of "Armor Value" states that "Motorized vehicles without a printed armor value have an armor value of -1 (usually trucks and jeeps)". So, technically, this indicates that trucks have an armor value, albeit -1. The Direct Fire Table, 4th Ed., indicates that an "M" check refers to "All units without armor values in target hex check morale (14.1)". So, if the definition of an armor value is in play, trucks would not check morale unless an "X" were rolled, in which case "All other units in hex must make an M2 morale check". Is one correct in assuming that DF will only affect a loaded truck if an "X" result is rolled? Or do players just use the  DF table as though the truck did not have any armor value for protection?