Most bicycle grips are simply glued to the handlebars using grip cement. This is fine as long as the end is left exposed so that a delrin handlebar plug is allowed to protrude.
In seriously wet conditions, one of the best choices for grips are ODI Lock-On Grips. ODI Lock-On Grips require a few modifications. Without champhering the end of the clamp, the glamp will get marred during use. This marring will tear gloves in time, causing problems and expense. Also, the end of the clamp can be made far more comfortable with the addition of a large champher.
Off the shelf alternatives
BlackSpire has one of the best accessories for lock-on grips. It is an end cap for the handlebars as well as clamp for the grip. If you can't do what I describe on this page, look into BlackSpire's quality canadian products.
Champhering the Clamp
This is how the grip clamp is in stock form.
Both sides shown.
The clamp is clamped to a shaft on the lathe and set-up.
Time taken so as to not damage the screw.
This is what you are looking for.
Modified clamp re-attached to the grip.