– Last Updated: Jun-24-07 3:38 PM EST –
I can see using something like those "Landing Pads" for mounting to the roof of your car. For a trailer, I'd only use those if you already have them. It sort of sounded like you'd be buying some for this purpose. I certainly wouldn't buy any just because they give you a way to bolt your cross bars to the trailer, but then, I'm a cheapskate about things like that.
You could find all sorts of ways to mount that round Yakima crossbar (or any other round pipe) to your trailer. The easiest way I can think of off the top of my head, would be a little "tower" made from 2x6 blocks (with short pieces, 2x6s would be less prone to splitting than 2x4s). Use a long block (about one foot) for the base, 2 or 3 short blocks stacked on each end of the long block to gain height, and another long block across the top. This way, there's a space below the top block so you can put a U-bolt through it, and that U-bolt (or a pair of U-bolts) will hold the round bar to the top of this little wooden tower.
(This was supposed to be a neat and symetrical little diagram showing how to stack your 2x6s, but there's something new built-in to this site that prevents me from inserting a controlled number of blank spaces in front of and within text. Because of that, the picture is a mess)
Bolt the towers to the bed of your trailer and you are all set. A similar rig could be built to mount the bars to the tops of the trailer sides, if the trailer has a cargo box.
Obviously this is a dirt-cheap way to go. You can certainly be more elaborate, and use building materials other than wood. Bolting vertical pieces of angle iron to the frame of the trailer would give you as much height as you want for your cross bars, and the cross bars could again be attached to the angle iron with U-bolts. You may need diagonal supports both right-to-left and front-to-back to build in the stiffness you need.