The 'other' OP responses are all correct and my intial post was intended to
discourage the OPer from painting or gel coating. However if he were to
proceed the effort would be worthless unless the glass surface were properly
cleaned.

My bilges were painted while the boat interior was still open and
ventilation was practical..

As a final note of caution. The interior of a polyester fiberglass boat has
a surfacing agent residue in the interior of the glass hull. This is a very
thin film of wax that floats to the surface of the resin during the curing
process. This wax film must be removed before anything will bond to the
glass hull. During the construction process it is customary to wipe the area
of attachment with acetone. However in a completed boat there are too many
low points and pockets where these fumes can accumulate and only strong spot
ventilation can purge these fumes.

There for I with draw my recommendation for bilge painting after the
interior is installed..


--
My opinion and experience. FWIW

Steve
s/v Good Intentions