There are two different sizes of 12V power outlets and plugs, size A and size B. Size A is what is usually used in U.S. vehicles, and size B in European ones. Size A is a little bit smaller in diameter than size B, so it can sometimes be a loose fit. I remember the dealer telling me something about an adapter sleeve one could get, but never pursued it. I've had marginal luck with bending out the side tongs a bit to make the converter fit more securely in the Rovers.
The RN price for the Front Runner load bars is the same as on the Frontrunner website. They're reasonably priced for what they are IMO. With such an expensive vehicle you want to use something too crappy, especially if there's a danger of them cracking the drip rail, and all the grief that will bring. If I was looking into having a local shop fab something, I'd be inclined to something that would clamp onto the roll cage; much stronger.