Sub Frame connector conundrum

What Rice Nuker said! Actually I've done them through the floors, attached to the floors or under the floors but always used at a minimum 2x3 .120 wall tube or even 1 5/8 roll cage tubing welded side by side. The rigidity was so good I couldn't tell the difference. The real issue is installing them. The floor pans, unless new, usually have suffered from some rusting over time making them even thinner to try to weld heavier gauge metal to. Plus this is all done overhead or on your back, unless your one of the "blessed" with a rotisserie. Your probably right that it is structurally stronger attached to the floor but i think it would take measuring equipment to show it. Is that extra rigidity worth the effort? I just built a set of underfloor connectors for my Duster. When I install them I'm going to weld a panel on top of my connectors where they're up against the rear floor board and try automotive panel adhesive as a way to connect the two (welded on the ends of course---I know someone would have asked). I'll let you know how it works.