Gwerty12.
Concerning the sheet to sheet longitudinal welds.
The 'butt joint' with thin material and using manual stick welding is not recommended due to difficulty in welding.
Weldingmike27 showed the sketch of a 'lap joint'.
The gap between the two surfaces should be in contact with one another.
Clamping, tacking, and slight hammering the tack welded sheets together, before welding will help.
Another option is an 'edge joint'.
Again, the edges of the two sheets need to be in contact.
http://www.spartanmechanics.net/images/ ... Joints.JPG
General note.
The heat from the weld will be absorbed faster into an edge of a sheet of metal, and slower into the flat surface of a sheet of metal. So when you have the 'lap joint', that edge will get hotter much faster than the flat surface. That is one reason the two pieces should be in tight contact, in order to allow the edge to lose some of the heat quicker. You will notice during your practice welding of the mock-ups, that you will be orienting (pointing) your electrode more towards the flat surface, in order to put more heat there, instead of on the edge. It is as if you were welding a single pass on the flat piece immediately next to the edge. While welding that pass along the joint, one side of the puddle will flow into the edge of the sheet. Once you get the knack of it, who will laugh about all those holes that you previously made.
Holes can be done with a patch. But again, placing a patch is an example of a 'lap joint'. Clamp, tack and hammer down the edge onto the other surface. Probably placing a support against the internal surface, may help you avoid deformation from the hammering. If you hammer while the tack is still hot, it will be easier.
Alexa.