Posted for Mafopp5@aol.com:

 Claudio,
 
 The tips were not designed to be filled with fuel so the strengthening of
 the main spar and tip joggle would have to be reviewed.  I would get in
 touch
 with Lancair if I were you because, to my knowledge, no other builder has
 fitted long tips with fuel.
 
 Dr Michael  A Fopp
 Home Office
 Email: Mafopp5@aol.com