Are you on a Lucas or Bosch pump?
If its worse in the boot it could be a number of things:
Lucas pumps had a habit of breathing fumes through the casing when the seals are on the way out.
Hose unions can leak without giving any trace - worth changing including those on the fuel filter. Good way to check this is to wrap the unions with electricl insulating tape, fuel vapours melt the adhesive making it a dead giveaway if it starts peeling off within a week or so.
The centre O-ring and copper washer holding the fuel filter together.
If your pump to PRV valve hose is an older rubber type try changing it for a modern braided one - also a common source of leaks.
Finally it could be a leaking gasket on the sender unit or a blocked, badly routed breather as these are just behind the boot under the deck.
Hope that helps [:D]
Check the age of the rubber
<b>Red 4.0 Litre V8 DHC Grinnall (with huuuuuge arches...!)</b>