I've used the Yakima BowDown:
https://www.amazon.com/Yakima-BowDow.../dp/B0012SA4QY
Only 'assist' is one end sitting on rack while lifting the other...
Looked at the ShowDown - as overhead lifting is more challenging now - but it doesn't fit factory crossbars (for another vehicle).
Our toad is a softtop 2 dr Wrangler - haven't found a good way to do anything on top with that one... The available roof rack (runs down to hard body to anchor) looks like it makes opening the 'partial' or full roof challenging... even when not carrying anything.