Romanizing bidental fricatives

[Qwynegold]

How would you guys romanize fortis and lenis (voiceless and voiced or something similar) bidental fricatives?

Surely a voiced one is not possible? Is it breathy? Anyway, maybe <f, h> if you want boring letters.

[Chengjiang]

Voiced is certainly possible, although only the voiceless one is attested as part of a real language’s phonemic inventory. <f> works, although I think I’d rather avoid simple <h> due to the language in question allowing a wide range of CC sequences and several other consonants currently being represented with digraphs that include <h>. I suppose <v> would work, though.