If anyone else is interested, here is a great site about spot welding using a MIG welder. Main problem is you need a good MIG with minimum 200A.
http://www.esabna.com/EUWeb/MIG_handbook/592mig11_1.htm
I think I already have one of those special tips so i will give it a test tomorrow and see how it goes. If it works it should save a lot of time.
If it does not wrk then I think I will use plug welds to attach the sheets.
I have heard about that sealing tape but I want to use the sikaflex as it is easier to put on and I am using it more as an adhesive than as a sealer.
I will silicon up all the inside for sealing.
