You should use a high quality servo for the bow retracting mechanism. For me, I like to all out on it and buy a BRUSHLESS servo, which uses a brushless motor instead of the brushed one. The servos from Futaba sound awesome to have. They are digital, have dual bearings, strong samarium cobalt magnets, etc.http://www.futaba-rc.com/servos/brushless.html
There seems to be no disadvantage to these, other than cost (that is a guess). They may not work with some of our electronics (that is a complete guess, I'm never tried).
You could use a electric motor to extend and retract the mechanism instead. Ether way, they are not that easy to build. Looks easy, sounds easy, feels easy, but in reality, they can be a PITA.
Have you read the article in the download section of Rouge Subworks? That article is a absolute 'need' if you really want to make the WTC yourself. I just read over it again, it has a "parts listing" in the back showing you where you can get your stuff.
I forgot to mention this, but just like Sub culture said, you will need retaining rods to hold the end caps on if you pressurize the the WTC. Or you can use a bayonet-ring to hold it on, these things are awesome, they are reliable, and you don't need to seal the rods if you use internal ones. External rods require space, although in most boats, there is plenty of room for these, and internal rods need to be sealed at the end caps, but they can be used to hang your tech rack.
Take some time and research how other people made their WTC. It will give you ideas as to how to make this thing.
The job ain't done when you are on the couch watching football 2 hours early.