Helmet covers, or not?

[Tarbicus]

I have seen some references to Caesar writing that, during an attack by the Helvetii, his men did not have time to fix the insignia, or take off their helmet covers. Does anyone know of any attempts to make such a cover, even though there seems to be no archaeological find at all? Or, to speculate how such a thing would be constructed?

I would imagine it would not be too difficult for a pre-Gallic type (Montefortino, Mannheim, et al), but the extended neckguard and browguard would make this *not-so-straightforward" for a later 'Gallic' or 'Italic' type.

Cheers.