Leave the welding to a pro. In a flash you could be looking at some HUGE ugly holes if you have not welded aluminum sheets. Are the welds or seams cracked? Worn thin? If it is just a few minor "non-structural" areas you should use Gluvit. That will seal it up and it is the right stuff for the job.
If you do have it welded and it still might have a few pinholes..... again use Gluvit.
__________________ "When you see yourself doing something badly and nobody’s bothering to tell you anymore, that’s a very bad place to be. Your critics are your ones telling you they still love you and care." Randy Pausch 1960-2008 The Last Lecture
To check it out properly and give the welder some clues, fill the hull with water and mark any leaks with some orange marking paint. The paint will make a nice halo around the leaks.
Get rid of the silicone!!! Scrape, sand and use heavy duty green pads.
__________________ "When you see yourself doing something badly and nobody’s bothering to tell you anymore, that’s a very bad place to be. Your critics are your ones telling you they still love you and care." Randy Pausch 1960-2008 The Last Lecture