The P38 is an amazing product that works very well on both car bodywork and wood. It dries fast and sands to a glass finish and no shrinkage. I have seen it used on car doors and once done you cannot tell, plus even with all the closing it stays put, downside is the smell and not cheap. I will look at knifing putty as the more tools in the box the more problems can be solved. The stuff I have not come across since the mid eighties is a brush on primer filler, also used in automotive and was cellulose based but produced a really great finish, just not around anymore and it was thick gloppy and green.