avoid poor paint/chrome casing, as the sea side wind will catalyst the iron to get rusted

those downlights u get in lighting shops that looks like stainless steel are not real stainless steel. there are very very few that is really stainless steel. SS ones are very expensive, so hardly any importers. what shape you looking for? round, square, patterns?

head down to any of the light shops, u get many varieties there, but chances r you won't get high end ones, just normal ones. but they will do, just choose those with plain white frames, will match your interior better, rather than those with all the frills. but do keep note that 4" will better fit 1 bulb, coz if fit 2, than lifespan of bulb shorten caused by heat. 1 bulb will not be bright enuf, so need to have more lights. to hv longer lasting bulbs, use PLC with ballast. use good quality ballast like Sova, Solex or Luxram. normal brands will hum after some time. but if u 1 easy fixing, then use screw bulbs.