I'm working on a tutorial right now, the bones of which is up on my website now in the tutorials section. Its a way to go yet - but 6 Nations Rugby calls.......
I'm not manipulating any isobath polygons. In marine mode Garmin has 5 different shades of blue as depth area objects, and white as the deepest, plus a light green intertidal area object.
Only cgpsmapper supports marine chart objects at the moment (AFAIK), of all the Garmin compilers available, the rest seem to be concerned only with terrestrial routing and hiking.
It really is remarkably simple to produce these Garmin charts, it simply needs some "type" information in the export from RM, and that's it.
I'm hoping to be able to use some of the overlay textures (separation zones etc) as bottom hardness, but we'll see how that pans out.
I'll have the basic tutorial finished tomorrow I hope.
T