Yes, thanks. I hadn't thought of just duplicating a terrain, as needed, to "cover up" any gaps revealed by camera movement. Funny how things seem so much clearer after putting out the question.
I did try changing the size of a terrain AFTER I had customized it. Bad-bad. It reset to flat, but luckily I was just playing with settings at the time, trying to get the feel for how to work the shaders to get what I envision.
These terrains are great fun, I am looking forward to the project.
Thanks again.