I kinda suspect the real
purpose of the hole had to do with something in the metal stamping or assembly at the factory, and it was left because some engineer thought it'd be useful to have a drain there - but quite like with the hole found many years in the spare tire well of car trunks, they put a plug in it to prevent the ingress of water from road spray
all speculation if it's not in the assembly manual .... what's a pretty safe speculation Tim, is the factory didn't put a round plug in an oval hole to leave a constant drain, if the only purpose was drainage they would have designed holes for drains that didn't require the extra cost of having a "not plug" or have made a round hole that fit some existing cheaper plug - OTOH, some previous owner of your truck who lost that odd shaped plug might have used .... whatever
Bill
