That is good news; your shop found a surprise inside. Having all four wheels checked and serviced is a really good thing to do. It rules out a lot of possibilities. Now you have a benchmark point; tracking towing mileage in the future helps determine how many miles have gone by since the last brake and bearing maintenance.
If the issue persists, the axle tube wire issue may or may not be there. You said a 2015 camper when new and over 20K miles. 7 to 8 years of time and 20K plus miles most likely have started some wear on the insulation in the axle tube. How much depends on how bumpy the roads were during that time which is an unknown. This can be part of your next steps plan if the problem persists.
These kinds of problems are a true process of elimination.
Let us know how it ends up by the time your trip is over.
John