Is there a clear explanation for the steps in painting a chassis of a plarail engine?

Are there any tutorials on youtube or other websites that explain how to paint chassis blocks black? I can't find any.

A
- you can simply take a brush and some black paint like apple barrel matte black and lightly brush a few coats of paint in thin coats until the chassis is black (this is what I did for my tender engines)
- There is a video online that shows how to do this, albeit in timelapse form: https://youtu.be/t1_XS6-_Ihc?t=173 

B
- you can disassemble the engine entirely and then do the exact same process as option A

C
- you can disassemble the engine entirely, mask off the bottom so it's just the chassis block, and then use spray paint (and primer) to paint up the chassis block.
- I typically don't recommend going this route since it's a lot more difficult, and way overkill for a simple 10-minute modification.