Make your own buy and sell decisions of course but I think you are wrong on several points on JMIH. First the notion that there is a lack of demand for boats conflicts with reality.
I would point to the backlog and sales at both JMIH and FPB as well as Brunswick who just raised estimates on strong marine sales. Industry wide things look pretty strong right now. I realize you are simply making extrapolations based on antecdotal observation they just dont coincide with actual numbers.
As far as cost trends in resins I haven't researched this one heavily enough to know precisely where they are going but some resin prices have dropped recently and increases in others is starting to see price resistance.
ICOC also said on their last CC they see resin prices stabilizing