On our '89 Fleetwood Southwind, we had the choice of cutting a hole through the wall in the dinette and reaching in sideways, or cutting the fiberglass shower wall around the faucet itself.
We chose to cut the fiberglass and installed the faucet on a faux-marble panel, which we then epoxied to the shower wall. We put other faux-marble panels on the other 2 walls to make it match. It looks good, actually.
No access panels on our model.
Bad design on Fleetwood's part