I have a place about a 10"x10" on both sides under the rear seat with rust holes pitted through.To fix this with new metal do I need to try and butt weld these patches or overlap them? If I overlap them how is the best way to fix them to where you don't notice the patches without using undercoating? THANKS FOR ALL REPLYS!

Do a butt weld if you can it will be better. Then you can smooth the weld and paint.

There are replacement pans available, and they are relatively inexpensive.