Floor pan welding

Hello from a newbie!

I am trying to replace my floorpans by myself (never done this before) and I have a few questions.

I have the pans out and I am going to have to grind off the old welds to make a nice flush fit. I have a few questions:
1)Is there any way to seal the spots between the welds so that moisture cannot get into the little gap betwwen the pan and the lip on the chassis?
2) How many welds are needed for a secure, safe installation?
3) What other jobs should I be considering since I have the body off the chassis? (Its a dune buggy, so the removing the body part is not a huge task)

[img]http://www.gunsnet.net/album/showphoto.php?photo=50642&sort=1&cat=500[/img]