Space is at a real premium in my boat(Alberg 30) but I am trying to insulate the V-berth. Funds are a bit tricky too, and I came across an article talking about attic insulation, and the lack of benefit vs expense of the bubble wrap/fiber fill reflective vapor barriers.
I found a single sided reflective barrier for a good price, double sided for not much more. 110 and 128$ for a 4'x250' roll. (vs 142$ for a 50' roll of reflectix)
The article also talked about the lack of radiant benefit unless there was an air space on one side of the foil, but on the hull side it would be more about the vapor barrier I think?
This plus 3/8" or a 1/2" of Volara closed celled foam sandwiched in between two layers like on frugal mariner would take up little space, and might give me a decent boost in condensation avoidance, and heat retention.
I could then do the fiberglass panel, and/or a mahogany ceiling.
Attic Foil Radiant Barrier - 48" Wide Radiant Barrier Foil - Solid/Vapor Barrier
Foam Insulation, Padding, Closed-Cell Foam - Volara