I have a similar issue with my 2001 Adventurer 32V,
One of my next tasks is to follow the wires from amp to speakers and try to find out where the problem is.
We have been using just the TV speakers but I like things to work as intended, so I have this on my list to repair before our trip south in Nov.
Please keep us posted on your progress & I'll do the same.
Regards and Thank You.
2001 Winnebago Adventurer 32V, Ford F-53, V-10
2008 Jeep Grand Cherokee Limited, 4.7L V-8 QTII
U. S. Army Vet, In God We Trust