I don't have any experience with Trinity or Rockschool but you should definitely check out the Registry of Guitar Tutors bass grades ([url="http://www.rgt.org/exams/bass-guitar.php"]http://www.rgt.org/exams/bass-guitar.php[/url]).
They are recognized qualifications and the advanced grades (6,7 and 8) count as UCAS points towards university.
You learn scales, arpeggios, modes, bass patterns in different styles, improv, various aural skills and much more.
Plus you only have to buy three books at the most and can take any exam you like rather than them all.
It massively improved my playing no doubt!