Forgot to say you can also run SS tubes thru the tunnel and flare the ends with Metric flare fittings I can provide.
You did not say what year you have, but up to 73 models Porsche used steel tubes that can rust over time. In 74 they went to white nylon tubes that turn brown and that crack & fail over time. Some time in the late 70s or early 80s Porsche went to the black Polyamid tube which seems to be bulletproof. I have never heard of any actual failure of the tube itself, only the rubber hoses that were crimped to the tubes.
Thats when I decided to make new ones with threaded fittings.
Len