I know a tad or tad a lot too late, but here's what i did if its helps at all.
I took carriage bolts and did some grinding on the tops to flatten them a bit on the heads so they would slide better in the railings. Railings have a cap with a torx screw that slides off. Bolts go through 1 inch square tubing cut down to width then through plywood that I covered in roll-on rhino lining i had left over from the sub enclosure I had built prior, with a oversized washer and nyloc nut with some blue loc-tite
This photo shows only five bars going across but added a total of seven for better weight distribution. Still use it to this day and still works great ! Just open the sunroof and climb up through.
I love using it and get props all the time when using it in the wild from people. My son and I have use it for OTR ( Oregon trail rally ) for the Goldendale and Dufer stages. Goldendale we could see the entire Maryhill course. Use it for the 4th of July fireworks, use it for when we run our brush-less Traxxas RC cars, thrown go-kart frames Ive got off of marketplace up top and ratchet strapped them down. Christmas time I put lights up and around it. I'm sure I'm forgetting some other times Ive used it but you get the point. Having the elevation and able to see so much more is so awesome. I did however have to make a custom bent open ended wrench to hold the carriage bolt when tightning it. I just used the thin flat kind that comes with furniture that you have to build yourself and then torched it hot enough to angle it right so your holding it out in the open and not under the plywood with little room whereas if it was straight. Hope this helps !
Whats crazy is that this picture was taken 13 days after this post. May 17th, 2024