Eternabond is a sealant for seams, used similarly to the way you would use caulk.
Unfortunately, roof damage occurs all too often, enough that there are online places dedicated on how to rebuild your roof. Other folks have done it and documented how they did their particular repair. You can check
here for a host of methods and possible costs.
I would also take this opportunity to identify the source of the leak since you'll be into the inner workings of your roof. If it was the Eternabond that failed, it would be mostly due to a lack of adhesion to the underlying surface. In my case, that was because of improper surface preparation the first time. I fixed that after removing it and doing all of the steps, explicitly paying attention to the prep instructions.
If the Eternabond was not the source of the leak, consider the roof vent or air conditioner gasket, if equipped. Other sources could be the corner caps and so.
Concerning is the "obscene" amounts of snow, which can be quite heavy. Having lived at the edge of the snow belt on the southern side of Lake Superior, even a foot or two of seasonal snow can be extremely heavy. It could have caused the roof to bow under the weight and when it started to melt, found a weakness in the roof and gotten in. A common failure point is the gasket under the air conditioner, if equipped. After melting off, it is possible the roof returned to normal shape and obscured the path the water found into the interior. That's purely conjecture, but just an idea to help you hunt down the source of the problem.
I know it's not the funnest thing to do after shoveling sidewalks and driveways, but get the snow off of the top of the PUP. As you found out, it can disastrous. I remember having to make the trip up to a church camp a couple of times each winter to help remove snow from the roofs of the structures to prevent damage.
As for insurance, only your agent can answer that question. You would have to have a policy specific to your RV for any coverage to exist, though. Homeowners and tow vehicle coverage would not extend to an RV without an express rider or addendum (probably only available on the house). I have a policy (for a while longer yet until the value of the PUP really drops) on the PUP specific to it that covers things other than liability, which is covered by the TV's liability coverage while being towed.
