Due to the complexity of fitting a hose from the evaporator, through the
inner wing, under the car and around the silencers and rear driveshafts I
want to install in 3 sections, any legal or safety issues doing this?

I HAVE* to go about 3-6 inches from a silencer in one place - any tips
there?

Petrol and brake run between silencer and floor.

*Cill / small gap / silencer / small gap / prop / small gap / silencer /
small gap / cill