Thanks for all the suggestions. The most helpful one for our situation is to get an exterior windshield shade, and I'll be pursuing that. I'll also pursue an upgrade to 15K A/C.
Here's what our situation is relative to most of the other suggestions:
About awnings:
I asked about adding awnings over side windows, but my service people say that’s not possible for this unit. The passenger side has a large awning, and that helps a lot but not enough.
About foil-covered insulation:
I’ve cut Styrofoam panels for each side window and taped aluminum foil, shiny side out, to these panels. That helps, but not nearly enough.
About portable AC:
I doubt I could run a portable AC without tripping the shore power.
About interior fan to move cool air:
We’re doing that, and it does help, but not enough.
About closing ducts:
Bathroom ducts are from rear air, which is cooling the back very well.
About curtains/shades:
We have good sun-blocking shades on the windows, and we keep them closed with the Styrofoam sheets between the shades and the windows. Shades help, but not enough.
About A/C condition:
Both units seem to be blowing cold air. The rear unit cycles as I would expect. The front unit seems to cycle occasionally, but runs most of the time.
About roof vents:
We do have housing covers over our roof vents.