I'm not sure if the following applies to your 4runner. The load bars on our truck stand 6'11".

Does the 4runner have a swing-down tailgate? On my p/u with topper, I can 1)set the bike against the open tailgate 2)jump onto the tailgate 3)pick up the bike and roll the back tire down the roof 4)attach the front tire at the rear of the roof 5)jump on the vehicles rear wheel to attach the rear wheel
This technique works with any carrier, including single bike carriers.
OR
with our Yakima Sidewinder head swung out, 1)support the bike in a vertical position with my shoulder in the frame 2)reach up with my other arm to connect the fork 3)walk the bike to the rear and climb the rear wheel to attach to the rack
Step 2 would be easier with a second person.
The advantage of the Sidewinder is that the fork mount part swings out from the vehicle. This makes it easier to get the bike mounted inboard of the towers, which is how Yakima and Thule recommend the carriers are mounted. It's also easier to fasten the rear wheel (or boom tube) inboard while standing on the rear wheel. It's very difficult if the bike is directly overhead-outboard.
OR
Put a carrier on the front of the vehicle. Probably not good on a smaller vehicle like the 4runner.
OR
Mount a carrier to the front of the trailer, above the tanks, mounted to the tongue. This would probably require custom welding. There was a Canadian mfr. that made these for singles, but I don't have any current info.

Anything mounted on the rear of the trailer will get well shaken. Search the RV forums. I wouldn't put our Draftmaster there. It will also add invisible length to your rig.

Happy camping!