I did it the hard way. The Explorer crossbars (circa 2000) have cross-tubes which can be separated from the towers. The easy way is to buy an extra Explorer crossbar, cannibalize the elliptical tube by cutting it into about 2-9/16" lengths, and TIG weld them to the ends of the other crossbars. I would've done that because I had four Explorer crossbars I bought on eBay, but I wanted four complete crossbars, and not just three. BTW, don't take that 2-9/16" dimension as gospel. If you attempt this, double-check the dimensions before cutting. It seems to happen sometimes ... no matter how much I cut off, it's still too short.
The way I did it was to contour grind eight (!!!) pieces of steel (aluminum would be better, but the steel was handy) to match the cross-section contour of the elliptical cross-tubes. Then I ground a step around one end of each so the cross-tube would snugly slip-fit onto the steel about 3/8". I drilled and tapped holes thru the tubes into the steel blocks, and secured the connections with stainless steel #8-32 machine button-head screws. Lastly, I secured the tubes, now with a fitted insert at each end, into the crossbar towers using more #8-32 stainless steel fasteners. If you've got a milling machine handy, this is a walk in the park, but will still require a lot of handwork.
