I love seatrout fishing at night, i spend a few nights on the Spey every year and there is no where i would rather be in June with the cairngorms in the background.
Everything Sewin basher has said is spot on.
Dont get complicated just keep it simple and fish the usual sea trout patterns.
Stoats tail and teal blue and silver do it for me.
Like SD said keep them sparse.
A good tip is to make up a few casts in daylight and keep them in your pocket.
I will be at the Glaslyn in July any tips Sewin basher?
I have been down that way the last two years but never tried for the sea trout there, it is a bit donting fishing a strange water on your own
Dont panic when you hear strange noises at night.
Tight lines!