We have the 337 also and have had it going on 1 year and 10,000 miles- 105 nights. We have stayed warm and comfortable in 5 degree/ ice storm (1/4 inch entombed the rig) and have stayed cool/dry in the humid Smokey Mountains and the plains of South Dakota. (2 ACs ducted)
Just put on Maxxis tires for our Winter trip in a few weeks. The only trouble we had was the Atwood Helium refer had some issues but Grand Design and dealer fixed w/out question. The Solora/Lippert awning had an issue pulling out on the first builds and that was quickly corrected. I hear they have got the bugs worked out but still (like any unit) do a thorough PDI...and buy local!! Makes a difference when/if warranty work is needed. JMHO