While looking for TSB's, I found that there is a TSB issued for both the FEH and the MMH, with a summary of "NEUTRAL TOW CAPABILITY -- SERVICE KIT REQUIREMENTS."

Unfortunately, one has to pay to read the full TSB, so I haven't. However, that summary makes me wonder if something, like the installation of some "service kit", needs to be done to allow one to tow a hybrid behind a motor home.