I made the tanks from 2.5 mm 316 stainless steel. I needed three sheets (8x4) to make the 4 tanks.
Two 20 gallon fuel tanks (40 Total) and two 60 gallon (120 total) tanks for fresh water.
I used a plasma cutter (thanks John) to blast out all the flat sheets. this was qui
ck and easy as you can use a straight edge (10mm ply) clamped down the the sheet metal and just run the cutting head down this. Far easier than angle grinding! I then use flap disks in a 4”grinder to remove what little slag is left from the cut. I had cut out all the sides in an afternoon. Then it was just a case of tacking all the sides together every 6 inches or so before seam welding it all together using a TIG welder. I added stiffening bars in the middle of the sides to prevent the sides bulging out when full of water/diesel.
I made 10 inch inspection hatches on the tops of all the tanks . Adding these and all the pick up pipes / fillers seemed to take longer than making the main tanks. In all these tanks took me 8 days to make which i think has been well worth while at this stage.