Your doing a great job - my only advice from my experience is bonding paste.
The work you are doing now is spot on but when you need something that is as easy to work as filler but you need less shrinkage, more adhesion and much more durable finish then bonding paste is great.
The stuff i used was two part, when its ready to use it changes colour. Its normally used to join fibreglass mouldings but i found loads of uses for it.
Keep the pictures coming - your inspiring all of us in this cold weather