I'm making good use of Custom Paths to define ledges, reefs, etc and these show up well on my Lowrance HDS. I use the thickness parameter to help "fine tune" my maps.

Would it be possible to have a "dot" or "dash" option for the lines drawn as Custom Paths?

You could have a look into the manual of IMC. There is a description, how to adjust and change line settings with QGIS. The basis for this is to export your lines as shapefiles.

This way is a little more input, but you will have the full capabilities of IMC available.

Thanks for the suggestion Hubert. I'll see what QGIS / IMC can do.