I did. First time was sheer luck. Then another time when I found out about the mechanics, I made a tile map of the entire route, and did the fish 3 times per tile method. After getting a few, I only kept a Milotic which I breed when necessary. Haven't bothered to find any in subsequent Gens.
I had to fish in every tile for that thing. I think I struggled as much with making it evolve since it was way easier to use Pokéblocks made with the Blend Master (only in Emerald) or with those high-leveled berries that took a while to grow which you can get by telling a special phrase to the Berry Master's wife than to use Pokéblocks just made with Chesto Berries.
Once I knew the method for catching Feebas, I thought the process of finding one was (very long and annoying, but) easy. But before that, I was a lost puppy who was only able to find Magikarp and Carvanha...
I looked at Pokedex and saw i didn't had a Feebas, so i checked its route and it took me like 10 minutes to find one and catch, then i said "well that was easy". Then i did some search on the internet and found out that he can be quite rare and "oh man i got really lucky then".
On a recent playthrough of Sapphire I decided I wanted a Feebas. I was determined to check every single tile until I found it, and lo and behold! I found one on the fourth(or fifth) tile I checked! So happy XD
I picked no. If I recall, I just simply charged through the route. It's been a very long time since I played R/S/E. Not even in the remake. I was happy with the team I had when I first played Alpha Sapphire. It was Swampert, Breloom, Manectric, Swellow, Camerupt and Latias.