Park on the infield, or turn left opposite the 'Chris Curve 2' box, go through the gate & park in the spectator area.

For bikes, at various points around the outside of the circuit.

There is a Portaloo on the infield.

An interesting post for bikes! Typical incidents are lowsides under braking at the entry, highsides on the exit.

Note: For Bemsee (probably other) bike meetings, Chris Curve is operated as one post.

For cars, just as interesting.
Be prepared to run away - if anything happens exiting Park (which it does), cars may take avoiding action towards the box on the inside, or otherwise end up with you.

Cars also can get a wheel on the grass on the outside and go off into the tyres. Although, if they're going fast enough they'll end up at post 9 (might need to help them sweep up at the end though)