If a secure fixing cannot be achieved a timber fixer should be fitted.
Sure edge gutter trim.
Check kerb trim install the membrane with a 75mm overhang on all sides hold the trim in position and apply downward pressure to ensure a watertight seal secure the trim with 50mm polytops through the pre drilled fixing holes note.
Gutter trim with built in batten gutter trim with standard batten backplate check kerb trim check kerb trim to gutter trim corner gutter trim external corner.