Well, having had a 1976 SeaCraft 18', I might as well weigh in on this debate.
We removed the large cowling around the engine on mine and installed a starboard splash "panel" that was about 10" high (much easier to understand if you go to
www.theboatzone.com/gallery/marklewis ) and put two brass 1.25" drain pipes through this that could be plugged when desired. These would drain water off the deck into the space surrounding the bilge pump access plate.
The bilge pump access plate was raised 3/4" by mounting it on a piece of starboard and then placing the piece of starboard over the original hole (an easily opening round hatch was used).
When the boat is sitting in the slip, no plugs are needed and rain or other water will readily drain out as long as nobody is standing in the aft area of the boat. Once people are introduced into the equation, plugs are a handy accessory.
The 18' is NOT an ideal candidate for the heaviest engines. While I owned mine it had an Evinrude 140 on it (396#) and later it was repowered with a Yamaha 130 (slightly lighter), either of which were fine in both weight and power. Both of these were mounted on a manual jack plate that placed the engine roughly 4" farther aft in order to make room for the hydraulic steering.