Swapping out king pin

Question: Would you want to make sure the pin box you're replacing is recommended for your 5er? Just curious...We had a really short pin box on a Coachmen and I was going to put an extended pinbox on and was told by Coachmen that they didn't recommend it, thus, I stayed with a slider hitch, (I had a short bed truck at the time)...Just asking if one should check with manufacturing if changing length is involved...