Hi
I like where you're going with this. I had the same thoughts myself, A safari rack for mine generally costs upwards of $1000 for a decent one, a little less if you attach one to your roof rack cross bars. I bought mine without the cross bars and was surprised that I would be looking at about $400 for the crossbars that only had a 100 lb rating. I decided to go the route of addressing the issue myself. I'd like to share my experience with you in hopes that it might help you decide what to do, or what not to do.
Firstly a few pics of the work...
Here is the top view with the faring and my old Thule soft carrier. I hurried to get this done before taking my family to Kure beach last July.
I just ran out and took this one to show how it rides every day. I took the faring off because I want to improve it.
I used 3/4" and 1" galvanized electrical conduit, as well as some 1" and 1/2" square stock primarily as the building material. It is a bit heavy, (I would guess between 50-60 pounds. But since I attached it directly to the frame I think my weight capacity is over 300 lbs, so I still have a lot of room for gear. I welded the whole thing together (caveat: if you weld galvanized steel, it is very important to do so in a well ventilated area, the fumes are really bad for you) and then painted it with truck bed liner.
I used the 1" conduit as sparingly as I could as it is heavy, but I was happy to find that the inside diameter was perfect for accepting the outside diameter of the 3/4". This made reinforcing the front and back easier and stronger.
The pedestals were tricky, but when completed felt very sturdy.
Again I took advantage of the inside/outside diameter coincidence to make a solid attachment. The bottom bolt is threaded directly into a nut that I found welded to the frame underneath the rain channel (I'm not sure if they are like that on all vehicles, but it's worth investigating because if nothing else, it will give you an opportunity to clean it out).
The trickiest thing I found with this project was that even though my rig looks like a nice square box, it is not. I found that the center pedestals were out and up from the line between front and back. I would say the old adage of measure twice cut once should be applied when designing this, but for me it was more like...measure twice, scratch head, measure again, draw it out, cut, weld, assemble, curse, disassemble, measure again, weld assemble.
I am proud of it, but it is a little noisy at highway speeds without the faring. Keeping the posts separate from the rack gives me versatility as to different types of rack I could make using the pedestals for a platform. I wish I was a better welder, because it was tricky welding the different thicknesses, also I would have loved to do this in aluminum. I also plan on making a tin-cloth canvas bag that will attach to it with compression straps to add versatility to what I can load on top .
I hope this has given you some ideas of what might work with your project, or might not.
I wish you better luck than I had!
Brent