99% of people just use solid core romex house wire without a issue.
Most RV's are built with solid core.
Not worth the extra cost \ trouble of stranded wire IMO.
If you drive your bus 100,000 miles a year, go stranded.
"Don't argue with stupid people. They will just drag you down to their level, and beat you up with experience."
Patently waiting for the apocalypses to level the playing field in this physiological game of life commonly known as Civilization