Update – I did a number of things, one of them seems to have eliminated the problem (two different 10 min test drives, reverse lights now work, and the fuse doesn’t blow).
I took apart both tail light housings. No rust, no frayed wire insulation, no loose connectors, the push-in bulb receptacles looked fine, bulbs looked fine (filament intact).
I noticed the ground pin on the tow plug (on RV bumper) was pushed in; was not the same length as the other 5 pins. Don’t understand completely, but replacing that tow plug seems to have fixed my problem. That ground pin must have been hitting some other circuit and popping the fuse when in reverse. The odd thing is this coach has 5 wires going to that round 6 pin plug (L signal, R signal, tail, aux power, & ground), no reverse circuit. Again, don’t understand, but doesn’t matter – seems fine now.
Thanks for the suggestions.
Cliff