It wasn't an Irwin but when installing the ram on my IOR era (pinched stern, little room) 38 footer I had to build a small platform to mount the ram assembly to. I started with a marine plywood
built platform by gluing it together, fitting/filing it to fit the hull
at the proper height, then removed it, completely fiberglassed it and tabbed it in place.
I had that boat for 10 years and the ram and platform still looked like a factory built piece. I painted it to help seal the glass and prevent moisture from getting into the plywood
It was forward and to the starboard side of the rudder
post due to space restrictions, it also made checking on it easier.