you can get threaded pipe in different sizes in larger sections if you want to custom cut your own cable channels. it's easy to add some o-rings for water and airtight installation.
edit : i've actually got a pipe threader to make my own. you can make your own and do different sizes with a good pipe thread set as well.
edit : i've actually got a pipe threader to make my own. you can make your own and do different sizes with a good pipe thread set as well.