Please specify year, make, and model of travel trailer you are using for better advice.
Any exposed water containing device will freeze solid in Pennsylvania. PEX tubing can survive freezing, but will not function until thawed. Valves, fittings, check valves, flexible hose, and other fixtures usually will be damaged if they freeze.
Even a TT with belly cover may not protect pipes from freezing. The cover must be sealed, insulated, and heated.
My Kodiak Cub was advertised as "All Season" with "heated and enclosed under belly". The kitchen water pipe froze in less than 4 hours when temperature dropped from 34 degrees to 29 degrees.
The dealer I bought the TT from spent $2500 sealing and insulating the under belly. He also installed three tank heaters.
I spent an additional two years and more money re-configuring the propane furnace system to keep the belly above 32 degrees and keeping the water pump from freezing. I also insulated the tank drains and dump valves.
The water pump was cracked. Keystone said it must be my fault and that in any case, freeze damage was not covered by warranty.
With three years of part time work and about $3000 I have camped in 17 degree weather and successfully dumped tanks afterwards.
I wish you good luck and happy trails ahead!