I have read various threads where people have repaired holes or gaps with expanding foam or the likes.
I would like to suggest an alternative if you come across any wood substrate whether it is in the roof, floor, etc.
There is a wood epoxy approved for use on historic structures (National Historic Register, etc.) called WoodEpox by Abatron. It is a non-liquid two part epoxy that bonds to a wide variety of surfaces. It is dimensionally stable and very resistant to chemicals, water, heat, and weather. Once cured it can be shaped, sawn, screwed into, nailed, painted, etc.
For example, when I patched the lamp hole in the solid surface top of the small side table behind the co-captain chair, I used WoodEpox to fill in and pack the bottom portion of the hole. Once cured I had a structural plug that allowed me to pour in and hold the epoxy that was being used as a plug to blend with the solid surface top.
Abatron also makes a product called LiquidWood, which is a two part epoxy that hardens and restores soft or punky wood from dry rot. LiquidWood can also make wood weatherproof by applying to wood that might be exposed to weather and water.
I am not affiliated with the company, but I have used both products.
Chris
I might add that West Marine has a product called Git-Rot. This is also a 2 part liquid that will stop wood from rotting. I have used this when replacing a small area in a difficult location is not feasible.
Thanks for the information. Epoxies, in their number of available, it can be confusing to select the correct one. Personal experience that you can gain from others here may save some errors on your own part. Thanks for posting yours.