I think i'm going to scrap and redo my enclosure i have already built :blub:

On a mk1 Fiesta (possibly the same for a mk3) the boot is pretty deep - and in front of that you have the area which is the tunnel for the fixed rear axle. Position the rad in the boot at a 45 degree angle - cut a vent out in front of that so that air is fed through the rad (via the face of the rear axle tunnel) and then add another vent in the floor at the back of the boot. Create a windage tray under the boot floor to help draw the air out of the radiator enclosure and vent at the back of the boot floor. On top of all this you also have vents in the rear windows to help expell the hot air out.

Difficult to explain - i'll do a quick sketch in a moment.