I've got a raised patio built out of retaining wall blocks. Rockwood 6 Classic. I'm going to be installing a vinyl railing kit for safety. I want to just fasten the railing post to the caps, which I think would be sufficient. But to make it stronger I got the idea to place concrete in the cavities of the last course of block, then secure the caps. That way I can use longer hardware to ensure I get a good bite for the anchor posts. Thoughts? Thanks.