You’ll need to do something for sure. A few weeks ago I foolishly put a knee down on the roof while trying to retrieve a strap from my middle rack. The result is that it seems to have de-laminated inside. I’ll try to get a picture at some point, but I’m a bit embarrassed at my stupidity.
If you built DIY beef bars you could affordably build supports to stand on by putting stringers from bar to bar. Thing to remember is that just like lumber; that rectangle profile is stronger for that type of load in the opposite orientation most DIY racks are designed.
I have 2 beef bars that I have 2 sand ladders (5 foot long) bolted on. My sand ladders are basically marston mats but made from aluminum. They are the old school traction devices, I’ve had mine for about 30 years. Besides a recovery device they work as a platform to strap things down on, I’ve crawled on them but never stood up and walked around. If I was to walk on it regularly I think 1 more beef bar would be all that’s needed.
I built a rack out of 8020 1"x2" cross bars. I then cut 1/4" aluminum panels that were full width of the cross bars, and fit them in the side slots between the cross bars. I’ve had 2 people sitting on the roof, and easy to tie down canoe, kayaks, or whatever still utilizing the slots in the top of the 8020 track. I had 1/4" aluminum mounting plates laser cut by send cut send to attach the 8020 to the built in t track on the GFC. I can send you the file. I think the mount plates were like $5 each, and the cross bars are like $60 for a 6’ stick through Granger, you can cut it to fit with a chop saw and a fine toothed blade. the 1/4" aluminum I had as scraps from a job, so not sure on the cost there. I am trying to find a picture, as I sold the 4runner that had the rtt on it. Pictures are from my newer setup, but same side plates, and cross bar setup.