I was about to say I don't recommend anything that can roll underfoot for jacklines, but I realize now you're asking about lazyjacks - a whole different animal.

you don't need a whole lot of strength for lazyjacks. They don't really take much strain except for the sideways weight of the sail as it gathers when you lower it. Chafe isn't really much of an issue either. I've used shock cord up to now with great success except that it has to be replaced often, so this year I'm going to try some nylon "small stuff".

I do think your plan is overkill, but it'll look great.

 

Yes; I should have written lazyjacks (jacklines for the sail). Can't change the title now...

The reason I was thinking of the lower stretch line because this is for a stack-pack so the pack will need to be supported when the sail is up; but yeah, I'm sure the dyneema is overkill.

 

Actually, dyneema is relatively abrasive as lines go. If you aren't a fisherman, you have never seen the damage that Berkeley FireLine can do to ceramic fishing rod guides, and it is a form of dyneema. It can wear grooves in the ceramic fishing guides over time and only rods with the newer Titanium Nitride coated guides tend to deal with it well.

1/8" dyneema would be great for lazyjacks, but I would worry about chafe on the sail.