A method for securing sandwich structures together, especially vehicle structures. In one embodiment, two sandwich structures are perpendicularly secured together, where a first one of the sandwich structures includes a micro-truss core having one unit cell geometry and second one of the sandwich structures includes a micro-truss core having different unit cell geometry. The micro-truss core of the second sandwich structure includes a micro-truss extension fabricated at the same time as the micro-truss core and having the same unit cell geometry as the micro-truss core for the first sandwich structure. The extension is inserted in an open area between face sheets in the first sandwich structure so that it abuts against the micro-truss core in the first sandwich structure.