I can only tell you the what the law says and what I've done in like conditions
If you can't move over.. SLOW DOWN... Now I know slowing 26,000 pounds of Motor home + towed is not small task, but that's what I'd have done. And in fact HAVE done.
Also. INCREASE your separation between you and the vehicle ahead. Not specifically aimned at you but here are some observations
Standing on an overpass. or sitting atop a 40 foot pole (Remotely there is a Camera on top of that pole. I was sitting in an office with a controller in front of me) I have "timed" cars as they pass a point,, Usuall time from one car passing to next is 1 second or less.
When I was in school they told me TWO SECONDS in some states that it the law.
THey have since started suggesting THREE seconds for cars and FOUR for motor homes and that is on clear dry pavement.
Knowing the reason for this. I FULLY Support the increases.
An additional second or two would have given you time to slow down, and possible even move over.