You can run wires up over the bulkhead on the passenger side, tuck them down the side of the bonnet hinge, in the panel gap for the passenger wing and they will apear in the passenger door shut, at the top of the door shut is a rubber grommet, stick the wires through this and your in. This is the way 90% of people with Mk 1 focus run their power supply for amps etc into the cabin because as you say its very difficult and the way i described is totally hidden apart from an inch or 2 of wire in the door shut.
32-34 PSI for tarmac