I don't know if a liner for a 41 is smooth or textured or what type of glass it is.
I'll assume it's smooth. Clean it well and scuff it down to remove any glaze. Spray it with a fiberglass sealer, prime it, and wet sand it with 600 or 400.
If it's textured then just scuff it with a scotch brite pad. It's ready for paint.
Acrylic enamel is fine.

Dan


Remember your freedom - US Veterans provided it.
101st Screaming Eagles