No. It isn't strong enough (unless you have a source of very thick-walled tube), and wouldn't bond into the boat very securely. But by all means use PVC tube as a former to make your own GRP tube using glass cloth and resin. That would work. I use this method to make seatubes on thin-walled copper plumbing tube.

Perfect, excellent, and most good.  All the answers that I like.

So many complications go into adding a wheel.  I really don't understand some of the things that are done on production boats. 

I am no expert on this, but on the (quite a few) boats I have seen with ‘inboard’ rudders and tiller steering, the rudder shaft is run through a continuous tube, solidly fitted to the boat. No stuffing box anywhere.

Arne

Okay - so I've pulled everything related to the old steering system out of the boat except the steering quadrant - which looks press fit in with a key and I can probably get off easy enough with a modified gear puller.

Question is: do I fabricate a new rudder tube that extends all the from from the hull to above the cockpit sole, and consequently above the waterline, thereby eliminating the rudder post stuffing box and one more hole in my boat?  Or do I simply extend the existing rudder stock creating another opening, now in the cockpit sole, in need of a watertight seal?

As I write that out the answer seems obvious... but that may be because I'm unfairly biased against holes in my boat.

This is a "no brainer", IMHO.

A tiller is much better for feel, for speed of applying helm when manoeuvring at close quarters ,for KISS, for taking up less room in the cockpit when entertaining, for use with servo pendulums and trim tabs. 

A wheel becomes necessary when a tiller doesn't provide enough leverage, and can't be lengthened. That point is often reached at a LWL between 35ft and 40ft. It might be reached in a smaller boat if, for example, it has a very wide unbalanced rudder, or the crew has little arm strength, but I doubt very much if that's the case here. If the boat were mine, you'd hear a resounding splash, early on in the refitting process - unless there was any secondhand value in the pedestal and wheel.