I have installed sound damping sheets in Brv doors, especially at back of doors speakers, sound was improved of speakers but sound damping will work better if used on wheels well or mudguards area, i also used PU foam filled in frame & mudguards area.
doors rubber like you can see in civic or city, results was good.
You can check all these modifications videos on Youtube Brv is very popular in indonesia, mostly videos are from there, i took all ideas from youtube,PU foam is easily availablr from hardware stores & sound damping sheets from any good car audio shop, rubber seal from Lahore rubber store montgomrey road Lhr.