If they're in the topsides, try Creeping Crack Cure on a warmish day. Epoxy makes a poor filler for hulls due to flex.
If they're up under the toerail, they are cracks in the gelcoat owing to the mild flexing of the chainplates, which fasten through the toerail and cause the toerail to work side-to-side slightly. This is not 'damage' unless you let it go; then the hull can take in water. Again, Creeping Crack Cure will be fine as it remains flexible.
If they're under the waterline choose a watertight filler and do them with epoxy, which other than new 'glass is the only thing I would trust. Inexpensive production sailboats (like our Hunters) tend to be stiffer below the bunktops than above them; so flex is less of a problem and the absolute tenacity and permeation of WEST epoxy is the safest bet. Just remember to seal with a barrier coating before repainting.
