hey up buddy hate to piss on your bonfire but as soon as you weld them chassis rails in, it will burn that lovely paint whatever best bet is to drill straight through the welds and through the boot panel as well, then plug weld the chassis rails to the boot using the hoes you drilled in the boot floor, then seam weld the rails from underneath as well.Seam weling is where you have an inch run of weld, then miss and inch, then weld another inch and so on
hope that helps buddy and get ya finger pulled out with it