A note of warning...

[The Natural Philosopher]

..a mild solution of bleach clears black lichens off most things, but do NOT use it in gel coated glass fibre... the test patch of the camper is now clean of lichen, but has developed goose bumps..

[Andrew Gabriel]

Not sure what gel coated glass fibre is, but ISTR that it makes GRP go brittle, which is the reason many washing machines can't take chlorine-based bleach. Outer drums are often made of GRP.

[harryagain]

GRP resin gel is very porous though it looks shiney. Best wax polished to keep water etc out as frost damage/delaminating can result. If you use silcon wax, it lasts the longest but makes repairs dificult. (Resin won't stick to the silicon which can't be got rid of.)

[stuart noble]

Is it the bleach or the alkali that is in most formulations? Maybe pure stuff e.g. Milton sterilising solution would work

[Brian Gaff]

Ah, textured you mean, very desirable. brian