Finally had some time to put up details of mounting the rack. I used a generic gutter mount aluminum rack sourced el cheapo on Craigslist. I removed the steel gutter mounts and upended them. Here's the overall picture:
This is looking front to back. Of course, the Montero's OEM load bars are curved while the bottom of this rack (like most) is flat. I just mounted it so that the rack is level when the vehicle is parked level. It means that the aft-most mount needs a larger spacer than the front two.
The vertical metal pieces with channels cut in them were originally the horizontal surfaces to which the rack is bolted; they're sort of a universal gutter mount that has a lot of adjustability for racks of differing sizes. At 90 degrees from this mounting surface is a two-piece clamping part that grips your gutters. If you have gutters! We used this part to clamp the Mitsu's load bars.
As you can see, I rotated the mounts 90 degrees, bringing the horizontal surfaces to vertical and bolting the mounts to the side beams of the rack rather than the bottom of it. Since this is aluminum rather than steel and I wanted a lot of strength and off-road durability, I used small pieces of 1/8" steel plate cut to short lengths (approx 1" x 3") and used as reinforcing backers for the nylock nuts that you can't see inside the rack. I wanted to prevent tearing out of the hardware mounted through the thin and relatively soft aluminum side beams.
You can see that the mounts line up fairly well, thus making good attachment points for shovels, fishing poles, awnings, etc.
In this slightly more close-up pic you can see that I used some polyethylene flat stock (white in color) to make small spacers/abrasion pads under the bottom rack beam. You can also see that I've wrapped the OEM load bar with some rubber sheeting similar to inner tube material in order to cushion it from scratching in the area in which it's clamped by the converted rack mounts.
Using a Dremel tool, I made relief cuts in the sides of the gutter clamps through which the OEM Mitsu load bars can pass. Because the gutter clamping hardware is not a very robust guage of metal, I fashioned reinforcing plates exactly like those I made for the inside of the rack's side beams. You can just see the edge of one clamped just under the head of the vertical bolt and its opposite number reinforcing the bottom of the clamp, just under the nylock nut.
Here's the aft-most rack mount with a wooden block for a spacer. You can clearly see the upper and lower reinforcing plates I made acting as clamps held in place by the vertical bolts. These reinforcing plates allowed a very strong clamping of the OEM load bars. We overloaded the poor, cheap rack; it carried a second spare tire, two 20-liter jerry cans of gas, a high-lift jack, and various miscellaneous stuff at times including yours truly using it as a camera platform. We beat the bejesus out of this rack and, while the aluminum rack itself starting coming apart after a lot of off-road pounding, those homemade clamps never shifted a bit.
The next rack will be steel, also a large one like this, but more robust and able to take abuse without falling apart. We now know that clamping to the OEM bars will be perfectly fine...they're plenty strong.
