Need advice on frame connectors

I'm going to fab up a set of 2X2 subframe connectors and weld them in front and rear. My car as it sits is sans engine and trans and the door latches are not on at this time. I have questions. With the engine out, will the weight difference matter? Do I need to latch the doors to keep everything stiffened up? Should I work with the car sitting on four ramps so the weight is on the wheels or on jack stands? It seems to me that having the weight on the wheels makes more sense. For you guys that have experience in this area, please educate me. Thanks, Drew