Cheers for the replies guys.
I had been using tyre levers to get the last bit of rubber on so will attempt it without them next time. Am still slightly confused how I can do a 50km ride with no issues, bring the bike home and then have the tyre go down prior to my next outing? A very slow puncture I guess!?
I've put the stock Giant tyres back on and fingers crossed, so far so good. The only issue I have with them is they aren't red and seem a little slower (might be all in the mind as my times/speed are pretty much the same). Would I notice a difference between these Giants and the Continental Gators?
With regards to a pinch puncture, would they be more common with the Rubinos (700x23) as opposed to the slightly wider stocks (700x25)?
Don't bother spending more money on other tyres and whatnot just yet! If it is happening for some reason other than the tyre itself, you will still have the problem.
Does it happen with both wheels or just the one? You are unlikely to get a pair of faulty tyres. If it is both, then I would reduce any issue with the tyre itself to be of minimal liklihood.
Some small objects are so small you wont feel them just rubbing the inside of the tyre, turn the whole thing inside out and check THOROUGHLY. This can be done more selectively if you do as others suggest and put the tyre on in a way you can reference back the puncture on the tube to the tyre (easy way is to line the manufacturer logo on the tyre up with the valve on the innertub), otherwise take the time to inspect the whole tyre, with it inside out.
Check the rim tape covers the spoke holes and doesn't indent into them much if at all.
When you seat the tyre back on with the tube in situ, pump the inner tube up a little bit so it takes shape but is still easily compressed with your thumb, then go around the tyre pushing it in sideways and looking between the tyre bead and the inside surface of the rim for points where it may be pinching the inner tube, go all the way round looking at an inch or so at a time, on both sides of the wheel before inflating the tyre to full pressure.