The last time I did something like this the 'standard' for engineering approval was the overlap as mentioned but then seam weld (complete all the way around) on one side, and then stitch weld (weld 1-2 inches, then a small gap then the next 'stitch' ) - the reasoning was that the seam weld would have the strength, but absolute worse case, if the stitch weld cracked, the crack could only travel the length of one stitch, not all the way around. If you do do it that way, do the seam on the underneath (even though it's harder to do) and the stitch on the top side, as it won't let water get in there (yes body sealer should stop that, but don't count on it 100%)



If the place you are taking it to are absolute top notch craftsmen, that's not an unfair price. I'll tell you one thing, take it somewhere 'cut price' and if they stuff it up, have fun trying to repair it and then put the tunnel insert section (possibly the second one if they stuff the original up enough!) in.