When I used to shoot the P320, I used, and liked very much, the Springer Precision aluminum base pads. They come is 0.25" and 0.375" added length. I used the 0.25" ones, plenty long enough, and no worries about fitting the IDPA box. For an extra $1 per base pad, they will laser engrave numbers on them (up to 3 digits). You can have them all numbered the same (why?), or sequentially, or any combination you want. They have models for the gen1 (round hole) and gen2 (square hole).