I have a NS Arrow U. Camper was built in June 2013 and for various reason I couldn't pick it up till September. We drove to the factory, from PA, where REX did all the set up and walk through. He suggested that we camp in nearby state park so that if we found anything we didn't understand or needed fixed he could take care of it while in IA. We came back the next morning to have a flakey light repaired.
Upgrades that I have done include: replace the RV faucet with new residential faucet, and added a 150 watt solar system, two AGM 100 AH batteries, and a Trimetric.
With respect to the roof, TPO is used on buildings all time and with proper maintenance will provide excellent long term service.
We have camped about 40-50 nights a year in all kinds of weather and the camper is stored outside. The camper has been rock solid and is extremely well built.
Bill