Hey Ken, I'm looking at doing the same ladder project. My '85 M15 transom seems strong enought but I would still use marine plywood. I would seal the plywood with resin for added strength and moisture protection, and then I would probably use 3M 4200 to do double-duty as both an adhesive and sealant against water penetration from the drilled holes. The only caveat I could see is the ability to adjust the board around as you line up the bolts through the holes. If the caulking sets up too quickly then you don't get a 2nd chance. So make sure it's a slow-setting adhesive. Not sure if 4200 would be right in that regard until tested. I have experience only with 4000UV and it's gooey but you could still make adjustments within a 20 minute span. BTW which ladder did you buy? 2, 3 or 4 step? Garelick? Windline? I'm thinking I'll go with the Garelick because the mounting pattern is over a smaller area to give me more flexibility on where to position the ladder. Can't be too close to the rudder but also if it's too far to starboard the boat will heel more to starboard while climbing aboard. Hope to find a happy medium center-point (that's why a small mounting footprint is good) and hoping the 3 step would fold up nicely against the transom without protruding too far over the top. Neil