Here's the main bass line for the entire song:

G-------------------------------
D-------------------------------
A-----0-020--------0-0-0-20-----
E-303-------3--303----------03--

A nice, simple, steady reggae groove, with an almost childlike quality to
it. You can add/remove notes as you like, but Tony pretty much repeats the
entire line.

Then there's the simple turnover into the bridge every now and then:

G-------------------------------
D-------------------------------
A-------------------------------
E-303-0-0-0-0-0-----------------