I don’t make any guarantees but this is how I load my kayak. I drive a Rav 4 too. My boat is an 18 ft, 60+ lb single. I use Thule crossbars and Thule saddles.
1 open the back door, the plastic trim on the door probably won’t support the boat, keep it open
2 I lay a piece of carpeting across the rear set of saddles and hanging down a little in the door opening
3 I lift the bow up onto the carpet in line with the center of the saddles
4 slide the boat forward
5 lift the stern pretty much level and let the boat slide on the carpet
6 you’re done remove the carpet and tie down your boat.
For full disclosure I’m 6’1″ and I can reach a little better that many. The weight is still a challenge. Depending on your saddles you might just want to slide the boat up with the carpet laid on in the center of the rack crossmember between the two sets of saddles. The lift it on to the saddles.
Whatever you do don’t put the boat in a position to slide off.
Two disadvantages on the roller in my mind are it requires a higher lift and I see there is a little channel in the middle of the roller but that might not prevent the boat going sideways off the roller if you are not perfectly aligned.
Anyway good luck with it. I would offer to demonstrate but I live in Sidney.
Barry