Waaaiit...you're not supposed to walk on the roof?!?! I've been carrying boats on my Eagle for a since I got it on a set of yakima racks that I installed myself. I opted for the tracks and instead of following the instructions of alternating and skipping every other screw-holes in the tracks, I went ahead and put a screw through every one of them. If I'm carrying sea kayaks or canoes, I'll tie to the bumper/steps, but I don't find it hugely necessary for whitewater boats unless there's a whole bunch (more than 2) up there.
When I need to get up there, I usually step from my rear tire to the bed in front of the camper, then up to the roof from there. I figure if the frame pieces that are holding the rack/boats are solid enough to hold boats (the roof is rated to 1000lbs, or so I've been told) then I'll trust them to hold me for a few minutes while I load boats. I only step on the edge/frame pieces...definitely not where it's not supported.
Cheers,
West