I bought a Sea Eagle SE370 inflatable and used it for most of the paddling season. It was OK for the price but as I said to my friend, it was a "gateway drug" :) Near the end of the season, I bought a used boat that is much better. The inflatable was slow and didn't track well. The new boat, a sit-on-top, is much better and I can keep up with my friends.
I saw a video on youtube that might help you.
I don't use that method, I have a folding ladder that I fully extend and lean on the back of my truck cap. I then simply push the boat up the ladder onto the roof rack. I then make the ladder into an inverted V and use it to adjust and tie down the boat.
Here's a link to the ladder I use:
Pull-Up Strap Handle Kit
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