I would not use bonding adhesives for these structural floor pieces. In my opinion these must be welded.
Also, I am assuming you are replacing the floor support braces under the actual floor panels? Mine were completely rotted off.
I used some self tapping sheet metal screws in many places to hold things together nice and tight BEFORE I started spot welding it all together.
I had no experience either, but you'll find you'll get the knack quickly. One thing to try and remember is that when welding a nice new thick panel to a perhaps thinner existing panel the chance to blow through the old metal is greater. You'll quickly master the technique of "rolling" the weld bead from the thicker panel into the thinner panel and releasing the trigger before it blows a hole.
Using the right wire and experimenting with the settings should allow you to do a respectable job! GO for it!
