This is a problem here in the states as camper manufacturers focus more about building campers for either the glamping crowd or the family of 4 with 2 dogs and a cat that want to just go hang out at commercial campgrounds. Most of our parks or commercial campgrounds are serviced by paved roads. I am sure you have noticed that U.S. manufacturers no matter who made them, all have similar floor plans, the trim level and interior materials change. Just like if they have all organized and set standards as to what a camper should look like and include. Whatever they can make quickly and cheap but the average buyer will only use it a few times and then it will sit parked.
Even the trailers that say off road are built just like any other camper with maybe a suspension upgrade of maybe the shocks or tires.
Here is a nice 4 season well built camper that tries to focus on possible off road use but I have my doubts. After a couple of years traveling down roads like you describe, I suspect the camper would be worn out.
http://outdoorsrvmfg.com/
The actual offroad camper buying community is a small niche crowd. There is no profit for large camper manufacturers to focus on. Other than importing one from Australia, New Zealand, or South Africa, where camping is all mostly off road, we are limited to having a camper custom built.
One Australian camper manufacturer has taken a unique step in the U.S. market. Black Series Camper is importing their campers partially built with electrical, plumbing, and interior finished in California. These are highly rugged, true offroad centered designed. They trust their structure so well they offer a 5 year warranty. One of the reasons they are imported partially finished is because of the different electrical and plumbing standards between the countries.
U.S. website
https://www.blackseriescamper.com/index.html
Australian
http://blackseriescampertrailers.com.au/
Once you have located a true offroad capable self contained camper, you are going to notice another problem, weight. Rugged and sturdy construction comes at a price not just dollar wise, but additional weight.
The Black Series 12 and 15 foot campers weigh 1000 pounds more than your capabilities.