For photography gear, 40-50% RH is recommended by dry-cab (or dry-box) manufacturer. Stick on it, they are spend money to do the research to slowing down fungus' growth already.
IMHO, it is better to use Dry-cab than Dry-box. Since blue silica gel contains Cobalt chloride (for humidity indicator), which is known as carcinogen. Better safe than sorry. I wonder when the yellow silica gel take over blue silica gel (yellow silica gel is not carcinogen).