From Rockler: Full extension with
weather-resistant components (Accuride 100# class). KV 75#
stainless -- the 18" are on sale for a very good price! Or the same slides from another supplier, at about $6 less per pair: my very goods friends at
Woodworker's Hardware. Best vendor I have, bar none.
An important issue for you may be a stay-closed feature: like
these. You'd sacrifice some corrosion resistance. Or you could go with stainless slides and arrange your own hold-ins. Easy enuf. Haven't encountered stainless slides with stay-closed mechanisms; if someone makes them, I bet they are dear.
The bottom-mount
epoxy slides are okay, self-closing as a rule, tho many are not full-extension and they generally don't notch closed as securely as a ball-bearing slide does.
For a very clean look, you could try fully-concealed
undermount slides. They give you a full-width drawer box, tho with corresponding sacrifice in depth. You can add the Blumotion device, which acts as a self-closer plus a moderately effective hold-in. (Never used em. Never had a client who could afford em!)