Pin box flexing

[Irish Mist]

I have a new to me 2011 Cougar 327 RES . I noticed as I was lifting the pin out of the hitch there seemed to be some flexing or movement where the arm disappears into the fifth wheel.. The weight on the hitch is supposed to be 1500 lbs .. So I suspect there should be some movement as the weight is removed.
Sorry if this has been covered before.. I'm new and full of questions
Thank you .

[cw3jason]

frame flex is normal up to 1/2in. watch for things like seam separation or side wall cracking, that would be abnormal.