hey stefan, just wanted to answer your pm from yesterday, but you were quicker! over the years i've found that the best stuff for filling larger areas and getting a good "connection" between the wood and the filler is called PONAL DUO (as the name suggests, it's 2k stuff as well). mix it up, apply it to the cabinet, wait for about an hour and then simply press it into shape. downside: you have to wait for another 24 hours (well, i guess half a day is also fine, but i always give it that much time) before you can sand it. believe me: that stuff is PERFECT but unfortunately also pretty expensive. nevertheless, well worth its money.
for filling smaller holes and dings on the cab i use automotive stuff from nigrinwhich comes in two different types as well: for smaller and larger areas. the good thing about that stuff is that it dries within minutes and can be sanded down after about 30 minutes, BUT it doesn't adhere to the wood as well as the ponal duo does and it's not really "formable" because it dries so quickly.
hope that helps!