Hi Richard,
you said you set ReadOnly="true" and do not want the edtior have the scrollbar. and do not want editor automatically resize when the content is large. So please example your requirement on detial.
If the content large than the editor height, what you want it to do? Hide? Delete? like overflow:hidden? maybe you have your special idea, if you can explain it on detial, it will very helpful. Maybe you can send me some screenshots to explain it.
Regards,
ken