New updates:
1. - I finally got the suitable vinyl for paneling the bodies of the cannons. There is a wide range of vinyl tape and isn't easy to find the appropriate thickness. I asked a friend who works in a signage company, and they use a type of very thin vinyl for cutting plotter. Too thin for my purposes. According to my friend, thick vinyl is poor quality and that's why they use the thinnest. I asked for a thicker vinyl and he advised me that they use for printing. Of course, only in white, but the thickness is right in my opinion.
2. - Once again I used my mini-lathe to make the Hanomag parts that go into the rear channel of the wings.
3. - I've also done the part from the Sealab kit that is like a gas cylinder and that is placed next to the wells of the internal motors.
4. - Finally, I've also done the grill shaped pieces from the Sealab that are placed at both sides of the inner engines.
For inner engines, I preferred not to use the same parts used in the rear engines. To me it makes no sense to use the same parts in both areas. Okay, all four engines are equal, but isn't very logical that the pieces are the same in two such different areas of a single engine.
Fortunately, there are two different type of internal engine configuration, so I can choose which I prefer without losing accuracy.
To make these pieces, which at first seem complicated, I made a simple template on a piece of wood and a piece of plastic that helps me to fix and align perfectly the four curved rods. I've also done a channel in the piece of wood with a hole in the center to hold the small parts that make crossbar. Once they are subject in that hole, and using the channel as guide, I can use a small round file to give the U-shaped at the ends of the crossbars so that fits well against the curved bars.
The small step I made in the plastic template helps me line up the crossbars.
First I use liquid glue to paste these pieces, so I can make small corrections and adjust their alignment perfectly, and once the unión is near dry, I further reinforced the area by using a few drops of cyanoacrylate on the bottom of such unions.
Thanks for looking.

Rafa