now  i  have another pb importing 3ds as a mech ground  work
but now  i try  to import different object and  oz generate all time a flat cube
i resume the what i want to do, i try to make an inside/outside  in a volcano.
in first version i  use a heightmap for make  the zone and make tunnel with a dongeon builder 3ds file.
but have when a try to use "split with a ground mesh".
(i suppose is due to a face too big )
i put  files 
here if you want to see.
after this i ll try to make  this directly in truespace ( i prefer it to modelling) ,
an a make  a big cube and use "substract" fonction for make the zone(see sample picture) but dont work have a flat  cube when import (see the picture) .
 
 
 
 
p.s. i'm working with oz only since 1 week dont know yet all functions