Yes, that narrows the options...Good points. The t-loader likely won’t work for me as we pull a camper when we take out our kayak.
My plan with the Tandem Island originally was use the T-bar and then put it in the back of the cruiser or trailer prior to hitching up. Bottomline the Tandem Island at 18.5ft and 145lbs is just way to heavy and big so I went the DIY Engineered solution...
Maybe the less involved PVC tube side load setup per the video above and use of existing roof rack is a route for you? Mounting the winch should be possible by having the right plate and some holes in the OEM roof rack side bars (be it they are not that sturdy). I know, it is a puzzle unfortunately. I kept looking at it and thought the T-bar setup would be enough, then went to the next level.
You can also get even more creative which I would not recommend per this dude's video. Complex yet some of it to flimsy for my taste. The music is probably the best part...