If you go to the Expedition Portal Forums under "Expedition Trailers", you will find extensive discussions about trailers that are suitable for taking off pavement. This includes actual 4 wheeling with a trailer as well as more rugged conventional trailers that can stand up to miles of washboard and moderate dirt roads as found on NFS and BLM land in the west. This is a topic I've been exploring for several months with my focus being on the "rugged conventional" trailers. Meaning, something one can stand up in with basic accommodations similar to what can be found in a FWC or ATC. Unfortunately, as far as "rugged" conventional trailers are concerned, the consensus seems to be that, with very few exceptions, there isn't anything built in the USA. However, it appears that there are quite a few options for someone looking for small trailers that have the potential to be towed on pretty gnarly roads without self destructing. These usually are designed as gear haulers, with outside kitchen set ups, maybe a pop up or out tent, etc. So far, the only one I've found that is remotely interesting is from Trailmarker Outdoors in upstate New York. More basic than a conventional trailer, but has potential and they build them to order. Unfortunately, a long way from the west coast.