Other than the obvious issue of exposed live parts and 110-3(b)('99 Ed)...what Code sections would you cite for having to keep the covers installed on circuit breaker panelboards??

Look at 408.5 and 408.18.
Don

OSHA 1926.403

Maybe a look at 527.2(A) should be considered also.

Temporary installation does not mean to be a hazardous working location.