Suggestion on how to scratch build a rounded cab

[Oldmopars]

I am going to be building a cab for a truck, it will be a fantom truck, nothing that exists in real life. With this in mind I have a lot of flexibility on the details. 

I would like it to be made out of as few parts as possible for the main cab. Details will be added, but the structure should be one piece to give structure. 

My thoughts so far are to mold it from clay, foam and clay, wood and Bondo, or foam and Bondo. Then I would either vacuum form it, or use fiberglass and mold it that way. 

The pictures below are the idea I am looking for, I am not going to replicate any one of these exactly, just the basic feel. Again, it will be a fantom truck cab. It will also not need a back, the back will be taken care of another way. 

Yes, it is going to be a Mercedes Truck. I am going to attach the "nose" to a trailer to make a 40 foot long truck. Like shown in this post:

I have found a Mercedes truck with trailer from Italeri that will have most of the structure I need as well as the drive train. I will be building the Nose on the front. 

What would be your suggestion on how to make the "nose" for this truck?

[Eshaver]

Start with Evergreene .015 sheet styreene. You an then strengthen this by building "Brace work at the top and bottom in the back . Usually, Super glue is the best adhesive to work with in this case . Two part Automobile body filler is helpful , but you may find laminating two, perhaps three pieces of .015 together to make a strong piece as a lot of sanding will make the Bondo "Lift "  I do Odd shapes all the time as i make a lot of 1-24th scale gasoline pumps . I also have done oil tanks on model trucks .

[Ace-Garageguy]

If you want a high quality symmetrical body, whether in scale or full size, you need to build a buck first. Without a solid surface plate and some sort of accurate measuring bridge, free-carving a symmetrical part like this is very difficult even for the most accomplished scratch builder.

A buck allows you to transfer exact shapes from side to side, which is essential to achieve symmetry.

What's shown below is much more elaborate than what you will need for the nose of these vehicles, which have curves in only one plane (for the most part), but you should see the basic idea.

Once you have a symmetrical buck, you have options. You can fill the ribs with clay or bondo, or skin them with sheet plastic. Then you can make a mold from that to make your final fiberglass OR vacuum-formed part.

It's a rather involved process...not difficult, but it takes many steps and much thinking ahead (my advice is derived from many years of scratch-building full scale body parts, and lotsa scale stuff as well, and master modelers like Gerald Wingrove use bucks for the same reasons real-car body builders do). 

Edited December 17, 2018 by Ace-Garageguy

[Gramps46]

I agree with ACE, build yourself a buck and then fill it with body filler from which you can then fashion a body.  The formers keep the shape symmetrical from side to side.