If you're planning on running the original option equipped Lee Jr wishbones on the side of the cabin house, the length of the outriggers is either 18 or 19'. I'd recommend going with the heavy duty version of the 19' basic poles.
If you're planning on hardtop mounted alternatives, I've seen many mention of supplemental brackets secured to the aluminum hard top frame to support the additional stresses that those types of outriggers impart. But I can't comment on what the right length would be in that configuration.