You could try a vent tank valve in the line to prevent fuel loss.
The link below might help. Of course you would have the cost of
an EASA minor mod to add.

http://www.newton-equipment.com/tank_vent_valves.html



At 20:12 18 March 2011, BillT wrote:
We recently purchased this a/c & really enjoy flying it.
However there
are two minor problems with the vent line from the removable
18L fuel
tank:
1) We initially put 15L in the tank & over a period of approx
10hrs
flying, we've lost 3 - 4L due to it sloshing about & draining
overboard. The vent line exits in the main wheel box, so we
end up
with an oily streak along the underside back to the rudder after
each
flight. The PU(?) vent line is approx 5mm ID. I was thinking of
inserting a restrictor in the line close to the tank, with an ID of
approx.2mm, to see whether this reduces the volume lost.
Obviously
we'll need to ensure this never becomes blocked.
2) The vent line simply pushes onto a metal tube, exiting the
top of
the tank. There is a miniscule leak at this connection, just
enough to
cause a petrol odour in the cockpit when you first climb in. I
was
thinking of fitting a small hose clamp to see whether it solves
the
problem.
Any comments or suggestions welcome. Regards, Bill