Filling in window openings

Boy am I glad I found this forum. I am living on a 1977 Pacemaker 32' and it has a lot of rot around the big side windows. I want to fill in some of the window area and then buy replacement windows. I don't want to spend a lot of money, and it is okay if it looks like a band-aid job. I just need practical. So I was thinking of getting some of the laminated honeycomb that already has a gelcoat on one side. But my question is HOW DO GLUE IT IN PLACE WITHOUT GETTING WATER LEAKS? Left to my own devices, I would probably cut it as closely to size as I can but leave about 1/8" room all around to fit into place. Then I would epoxy coat the receiving areas and let them set together. Then I would basically butter thickened epoxy all around the edge of the new piece like peanut butter, and insert it into place, scrape off excess and let it set. Then I would put some epoxy around the outside seam to make sure it is sealed, and put some epoxy with wet fiberglass cloth on the inside to glass up the seam and give it some extra structural strength. Am I on the right track? Advise please!!! Another option is to make the insert piece bigger than the opening to fill, and make a rabbet joint all around so the new piece and old substrate interlock together.... Thoughts???? JIM

 

You need to address the rot to the window frames and surrounding structure and walls first otherwise no matter what you do its not going to last and you will be back fixing it again and again.
No you can't just "butter" in the replacement panel. It needs something to butt against and then be glassed over. Preferably a tab of half the surrounding thickness (your rabbet joint) which you can glue and screw the replacement panel to and then fair smooth. Could even be just a 1x4" "frame" between the old structure and the new panels on the insides.
You can probably get by with using marine plywood instead of hexcel, esp. if you have to remove a significant portion of the surrounding skin. Then you are glassing and fairing the whole thing in one go.