Hi, just to know: why not use several Thyratrons in parallel, instead of this Spark-gap switch ?
(or even a crossatron, but newer technology will likely cause more problems)
Thyratrons and spark-gap switches are apparently close together technically speaking (both use a ionised gas to trigger), but Thyratrons seem reliable, at least much more reliable than spark-gap switches given your descriptions. They have been used since many years in the industry with success.
Sorry if the answer is obvious for you, I am not a plasma specialist;-)