New trailer. Where to weld the D rings?

I just bought a new trailer and need to weld in some D rings. Where did you place yours? I have a Big Tex 18 footer.....

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A friend suggested welding them on the outside of the side channels like so:

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Also, I've heard conflicting advice on how to tie down vehicles. Some prefer to criss-cross the straps, some just tie straight forward and straight back.
YouTube has some videos that show all sorts of ways to attach the straps.

I won't be hauling 8000 lb tractors with this thing.....just cars. The rating is 7000 lbs and the trailer is right at 2000 lbs on its own.