Not many panel beaters are willing to undertake rust repairs these days, as it's not worth it for them to do so. In fact, I don't think any are.
I used to work in a car yard in Melbourne back in the 80's, and the boss taught me all about repairing rust, panel beating, spray painting etc.
There are a few different ways you can go with repairs, depending on how big the affected area is. If it's a large area, and assuming you can't find a replacement panel, or the panel is fixed, your best bet is to cut the rust out, or grind it out, and weld in a piece of sheet metal with similar gauge thickness. For smaller affected areas, fibreglass matting and resin are your best bet. Once again, grind out the affeted area, treat it with rust converter if need be, then apply F/G and resin, and finally filler for the final shape.
For the smallest areas, fibreglass filler is the best choice. It applies like normal filler and once hardened, can be shaped with regular filler.
I'm sorry to say mate but, I have the patience, just not the time. I work longish hours during the week, and am busy most weekends.
Try looking for tutorials online. There would be plenty with good advice. That's all I can offer you.
Best of luck.