STI carry mags

I am having a custom STI carry gun made in 40SW. I just bought a couple of preban 126mm mags and am in the process of rebuilding them. I use an SV for IPSC and am using STI tubes, Arredondo followers and springs with Berquist base pads. My question is, what guts to use for carry. The arredondo followers give me an extra round, but are they reliable enough for carry? Also, who makes a good base pad? I have use arredondos before, but managed to break them. I would like a low profile plate that will minimize the size of the mag.