Disclaimer.  I am not professional and there is a possibility that I have no clue what I am doing.  I hope that I have put enough info together to give you a good I idea of the steps that I use to create single hump fenders.  If clarification is need, please let me know and I add info/edit as required.  Sorry for not taking a few more/better images.  Hope this helps! 

1.  Begin by cutting a 1 15/16" round disk from a sheet of .040 sheet styrene.  I used a bow compass with metal points on both sided to get the job done.  If you use this method be sure to make the center hole the same size as the compass point; if it is larger you will not get a symmetrical disk.

2.  Mount the disk on a Dremel cutting wheel attachment. (The image below shows two mounted but one is fine.)
 
3.  Begin to round the outer edge of the disk using a rasp of other coarse file, sanding stick etc.

4.  Fine tune the chamfer of the outer edge of the fender with a sanding block.  I used 220 grit sanding paper.

5.  Finished disk on the right.

6. Before performing this step make a mark that divides the disk into two equal halves.  Then cut the center out of the disk leaving a 5/8" circle and then cut the circle in two.  You will then have two "C" shaped pieces as seen in step 7.
7.  Glue a .060 x.040 styrene strip (SS1) around the outer edge of the "C".  One of the .040 sides should be glued to the "C" and the strip should extend beyond the end of the "C".

8.  Cut a hole with the same diameter as inner hole of the upper fender wall (UFW) above from a sheet od styrene and layout and cut the lower fender wall (LFW) as seen in the image below and the image in the next step.  (Sorry for not taking better pics of this part)

 9.  Glue the LFW to the UFW and SS1, and cut the ends off SS1 off at the lower edge of the LFW. 

10.  Cut the lower portion of the LFW to achieve the desired fender height.

11.  Glue a .030 x .250 strip (SS2) inside of SS1.

12.  Make another side just like the one above.

13.  Cut two strips of .020 styrene to the desired fender width (don't forget to account for the width od the sides) and long enough to wrap around the outside of the fender.

14.  Beginning at one end, glue the first SS3 to SS2, wrapping it around the outer edge of the fender as you go. Be sure to keep the seam between SS3 and SS1 on each side as tight as possible. Cut the ends even with the lower ends of the fender side walls.


15.  Wrap the second SS3 over the first SS3.  Again, keep the seam between SS3 and SS1 on each side as tight as possible and cut the ends even with the lower ends of the fender side walls.

Construction complete!

Fill and Prime

Paint

Repeat x4.
If all this seems like too much work, you can purchase a resin set in the Parts Store. 

--Casey
 
 
 

I just wanted to make a quick note to say thank you to the admins at Model Truck Discussion, Model Truck Mafia, Building Big Rigs Tips and how did you do it and Model Trucks Other Than Pete or KW for allowing me advertise MTB.com  in their Facebook groups.  Thank you to those that have given me permission to post images of their builds in the gallery, to those who have added their own images and to those who have posted in the forums. Finally, thanks to all who have visited and/or registered.  I hope you find your way here often, contribute content when and where you can,  and most importantly, find the site useful and enjoyable.
Please do not hesitate to let me know what I can do to make MTB.com better.
--Casey

The Build-Off Peterbilt is getting close to completion! I have the hood functional, the mirrors are on and I made a big bumper from styrene. All that's left is the fenders over the rear wheels; I'm still not sure about the definite style and way of attaching them, but I have some time left to figure that out. License plate decals and IFTA decals are last. The stack tips are in place as well, but I'm not really sure If that was smart. I might have to work on the underside of the truck a little for that. Oh well...

I'm sure that I'm not the first one to do it this way but I was looking for an alternative way to stretch a frame versus  butting the ends of the cut frame rail sections against one another and lapping a strip of styrene over the joint.  Here's that alternative:

At the Joint of the frame, remove the shaded portion of the frame rail ends as shown below.

On one frame rail section, remove the center of the vertical portion of the rail leaving the horizontal portion intact (left). The length of the portion removed is not critical, 3/8" or so should work. 
On the other frame rail section, remove the horizontal portion of the rail leaving the vertical portion intact (right).  The length of the portion removed should be the same as the length of the portion removed from the other frame rail section.  Note:  Do not remove the horizontal portion by sawing along the inner edge of the horizontal portion of the frame rail, you will remove too much material from the tab.  Carefully cut the horizontal portion out with an Exacto knife, etc.

Connect the two sections like puzzle pieces and glue.  I use a straight edge (in this case my miter box) and a flat surface to align the sections and keep the rail straight while the glue dries.

Once dry, you should have a strong, straight joint that requires very little filler and is more realistic than the lap joint method.

Hope this helps,
Casey

Backdating the hood on this kit isn't as tough as one might think. With the proper tools, and a little patience, this conversion is quite simple.

First is to prime the hood to see the markings for the cuts, I drilled two holes in the top of the fenders for corner location. The first cut with a razor saw was along the hood upright on an angle to the bottom of the headlight buckets. Second cut came in from the side, at this point you should be meeting with the drilled holes.

The first cut with a razor saw was along the hood upright on an angle to the bottom of the headlight buckets.

Second cut came in from the side, at this point you should be meeting with the drilled holes.

Now that both buckets are gone I lined the inside of the fenders with sheet styrene cut to fit, this creates a foundation for the putty to lay on. Everyone has their favorite brand, mine just seems to be squadron green and white.


Starting with the green, put more than enough on and go past the ground zero, this will help in the end results.

After the green is sanded off, you should have noticeable low spots.

Now comes the white, I'm using two colors as a guide to see how deep I'm going into the fender

Once this is sanded off, do a quick mock up to check your work. At this point more primer will be applied and small defects will be cared for prior to paint.