Whats the best insulation for cabin voids

[Fender Stratoplaster]

What's the best insulation to put in voids around cabin doors like shown in the picture attached?

Feel drafts coming in the winter I'm sure is coming from gaps like these... normally there's a trim that covers this gap, it must do some job keeping the wind out as there were some nice big false widows nesting in there but I'm trying to minimise any draft I can

Would some foam weatherstrip be good enough or does it need proper insulation like rock wool?

Bit nervous about introducing a moisture trap and causing wood rot

Cheers

 

[Deluks]

If it's a small gap, try 'sealant joint backer rod'

Exterior grade mastic over the top.