Patching holes in transom

[Surfnski]

I'm thinking about removing my swim platform so that I can add trim tabs, I'm pretty sure my platform brackets are going to be in the way of the actuators. This boat is pretty stern heavy with twin I/O's and this big swim platform isn't helping any with getting the butt out of the water. So my question is: what is the best filler/material to use to patch the bolt holes once I remove these heavy stainless brackets? I want to use something that will be easily paintable once I get the transom repainted.