I put together a system a few years ago for use doing offshore surveying in the surf zone. The system is carried on the back of a jet-ski type PWC, and has to withstand constant salt water spray and splash, as well as occasional immersion. It consists of a PC, a monitor, an ultrasonic depth gauge, a GPS receiver, and a custom keyboard, all mounted on the jet-ski.
The case is an off the shelf Pelican waterproof travel case, with all connections in and out of the box through Seacon waterproof bulkhead connectors and plugs. Because this thing is in a sealed black plastic box used outdoors in full sunlight, cooling was an issue. It was solved by using a seawater cooling loop supplied by a tap off of the propulsion jet on the jet-ski pump. The monitor is a 9" TFT mounted in a smaller pelican case with a viewing window up on the handlebars, with the UI handled via a custom 12-key "keyboard" constructed from industrial watertight switches in an IP68 enclosure.
System is still in regular use, with the only repairs being damaged cables when the driver flipped the jet-ski in harsh surf and ripped things physically apart.