If you have trouble, as I do, cutting a straight line with tin snips, and you need to cut the long strips of aluminum for your seat, I have another way. I have a 1x2 screwed to one edge of my work bench. This allows me to take a 2x4 sheet of .016 aluminum and have one straight edge assured. I have a 4' aluminum level that is 1" wide. With the aluminum sheet place on the work bench positioned with one end flush with the end of the work bench, and one edge against my 1x2. I place the level on top positioned the same as the sheet of aluminum and then clamp it down with two bar clamps, holding the aluminum sheet firmly against the bench top. I purchased a scribe made for scouring plastic sheets. I used it to scribe a straight line by pulling it along the edge of my level. You can use anything with point or edge to do this, but this works really well cutting little curled aluminum chips. I didn't know this, but it is ok to use wood working tools on aluminum. After making a few passes using some force, I gently lift the aluminum and bend it back and forth and it will brake right along the line you just scribed in the sheet. The deeper the scribe, the easier it will be to brake off the aluminum strip. After a couple of strips you will see just how many passes you need to scribe before you start bending it back and forth. On your first strips be genital.
This will leave some sharp edges on the strips, but you can file the burs off, but I like to use a rotary wire brush in my drill press. Make sure you are wearing eye protection and gloves if you do it this way. By holding the strips horizontal, and hold them in the center of the brush rotating in a direction that pulls on the strip, not pushing against, it will clean up the edges just about as quick as you can feed in the material and leave a nice smoothed edge on both sides as well as the edge itself.
If you have a sheet metal brake this process works even better. Works well for the ribs as well. Cut all my seat strips yesterday and they all came out perfect.
On my seat I interlaced the cross strips so they come out under the two outer vertical strips and cut them off flush the with of the seat. Should you bend them over and the bend is up, you have something to catch your cloths or skin on when you slide in and out of the seat. I will also install a couple of diagonal braces to the front seat tube down to where the gear brackets are. When I got in and out of my seat I noticed the front bar was bowing. I'm a little heavy, so maybe the braces would not be needed if I were lighter. They were on my DE.:enjoying: