#1 - Lay and support the fenders on spacers (3" mine) on a flat bench.
#2 - Check with a square where it touches the fender.
#3 - Cut 18 gauge strips 6" + or - for 3" tub.
#4 - Make sure the width does not exceed the radius, just inside (you want the least amount of filler).
#5 - Trim the rear same as #4.
#6 - Tack weld
#7 - Repeat step #1 on trimmed 18 gauge steel sheet.
#8 - Weld trim and grind.
#9 - I fixed the 3" x 1" ID pipe spacers over each bolt hole and left the original fender flange in tact.
Very easy and solid for a greatly improved rear look. I was unable to find anything for tubbing these fenders and hope this helps anyone interested in doing this.