Neil. What do intend to photograph?
In all my trips to various places there, I have found long telephoto to be the least used.
That 18-135 sounds like it might be useful for most of what I can think of: landscape,
street scenes, people shots... At a pinch you can fit in some interiors of buildings.
As for your fear of changing lenses for much time, you may well obviate the need with the
aforementioned lens. However, there will NO DOUBT be the ODD occasion where you will
kick yourself for not taking just a wider lens. Now, which is worse?
If you think that you might succumb to a second lens, then IMO the one with IS is it.
Anyway, what if some of your gear breaks down?