Having a lot of experience raising stoopid amounts of weight it is hard to offer advice without a better picture of the situation. Being a sailor and ex-kayaker davits spring to mind but they might have their shortcomings.?
Also being a strong believer in the KISS methodology I like the idea of a pulley on the rear to get that as high as possible. Then you can use another pulley at the bow. The downside to this is the boat would scrape the side of the camper unless you had a shipping blanket hanging down from the rack. You would also need attachment points for those pullies.
Another half-baked idea is one pulley suspended from the two racks right at the edge of the roof. This would need a ladder of just the right length to act as a ramp of sorts to avoid scraping the side of the camper. You would hoist it right up to the edge, lock it off with a yachting or climbing cam lock, climb up the ladder to push it over the edge onto the rack and secure it.
If it was me I would have those racks much further apart otherwise I would worry greatly if the bow wasn’t tied off and that would entail more fussing.
It’s good to be a n00b - so I can aspire to be just stoopid.
Monrovia, CA
