Leaning Post Installation - 18SF

[duncansf75]

I have a '75 18 foot SF and I recently purchased a leaning post that I will need to install. It has two feet on either side that are spaced about 28" OC apart. The question is: when I drill the mounting holes, will I drill into the stringers and/or the foam in the stringers? Ideally, I would be inboard of the two stringers and could easily install some mounting brackets under the deck (the boat is in winter storage right now and can't get access to measure it). So I will take any suggestions for a sturdy install. - Thanks