Did you put any sealant around the holes after. Also how far apart did you space your rod holders?
Spacing might be different depending on how many setups you plan on using, longer rods and shorter, and when spacing them I would recommend putting some tape where you think you might want them and running it for a trip or two to see how they would feel. I still haven’t mounted my holders on my boat yet and glad I didn’t BC what I thought was going to be good in my driveway wouldn’t have worked out that well on the water.
Fasteners are stainless bolts and washers, nylon lock nuts if it’s going to see water at all especially in the transom and anything mounted flat on the deck gets marine grade silicone through the entire hole that way when the bolt/screw gets tightened it will come out both ends, might be overkill but makes me feel good.