To create a custom door panel fibreglass speaker panel will require a lot of job, but here, you dont have to make any mould.
You need to make a necessary wood frame for you speaker to sit on, where do you want them to sit, which angle should they face. So basically, the idea of using the fibreglass is to make the cover over it hidding all the inside wood work.
Like I said, after making the frames, apply the fibreglass over the frames. How do you do that? I am not very sure how much can you access to firebglass materials in Malaysia, but over here, you can purchase the over-lay clothes for fibreglass fabrication. Basically, it's a piece of clothes not any ordinary clothes but the texture and material is like a clothes, it's flexible, so you can stretch it over the frames and glue/staple it to the wooden frames, hence showing how your fibreglass surface would look like at the end.
After over-laying and covering the frames with the clothes, just apply fibreglass on top of the clothes and then you are done. Of course the surface would not be smooth, so a lot of sanding and fibreglass putty has to be used to create a smooth end results.
You might want to try using normal clothes if you cannot get access to them, but make sure the fibreglass resins does not eat up the clothes, otherwise it shows that normal clothes wont work.