collapsed a/c return ducts

[joe direnzi]

Fourth month of camping in our 2018 3721rl.Everything going great ,knock wood.Two nights ago, the fwd a/c started cycling off.Fan running ,compressor off.I have read different treads about collapsed return ducts.Took grills off and found the ducts were collapsed.Is there a previous tread that explains what size pvc pipe to use and what length and type?Btw a/c discharge temp.36 degrees.Believe a/c freezing up with restricted air flow.Thank you all