FFF,
Not sure I can add anything on legality or safety to what people have said above. However, you asked about the safety of the actual main fuel tank(s).
I'm pretty certain your Europa was designed and certified to JAR-VLA. The requirements in there are that the tank must retain all the fuel and stay supported within the aircraft at loads of 3g upwards, 9g forwards or 1.5g sideways. Also, it's got to retain fuel on landing with (I quote) "the most critical landing gear leg collapsed and the other landing gear legs extended".
There's an extra requirement which doesn't I think apply to the Europa standard tank but would almost certainly be applied to any ferry-tank or "baggage" fit in the back of the cabin that it's got to hold for 15g load in the direction through the cockpit.
G