I would draw the tube chassis using 3D sketch and weldment profile.
insert this into an assembly, then with placement of planes you can draw in the sheet metal parts in context with the tube frame allowing for future changes.
for the bends/folds I would manipulate the hem feature to get the wrap you need.
Hope fully I have attached an example assy below
SM_Weld Assy.SLDASM.zip 73.4 KB