Hi,
I'd keep the Arduino and LCD together..
1-wire communications is 3 to 5V and so has decent noise immunity. Thousands of "waterproof" DS18B20s like THESE are used in industrial systems without problems.
In a truly intense electrical noise environment, you could add a braided metal shield (grounded back at the Arduino) . You'd want to insulate the outside of that if it could contact any metal, which would cause ground loops..
I run the longer cables around the house, outdoors and to the swimming pool without problems..
DISCLAIMER: Mentioned stuff from my own shop...