BEWARE. I think that the bathtub thing is great for leather only, unlined boots. Don't even try that with lined footwear... much less with GoreTex or any other kind of membrane lined footwear!
I owned once a pair of military boots (look alikes, not the real McCoy like the ones you can get in USA) and they where great... and unlined. Then I bought a pair of Bestard Army model... somehow I got them small and I ended up selling them. Oh boy! Gore tex lined, fully gusseted tonge and warm. I would try the bathtub thing with the first ones but never with the pricer ones.
Mikel