Railings

This is a small job. I have a two-step railing (just one side) that needs to be installed on a trex stair to a deck, with standard pressure-treated stringer. The rail post has screw holes about 2.5 inches apart while the stringer is only about an inch wide. I need the railing to be firmly attached so it is safe for my 80+ year old friends. So some pressure treated blocking is needed below the stairs to attach the posts into wood, not just basic trex. I have pictures and am happy to explain this more clearly. I have the railing so all the material needed is the blocking pieces. This should only about an hour.