Maybe, maybe not. I expect to see trailers come with range extender batteries (very useful for RVs where those batteries can also provide power for whatever you do when there) this means ports on the back, but those will not be accessible when towing so you want one in front too...
The important thing to take away from this is we are still figuring out details and so should not lockin yet.
Honestly I think that RVs are kind of a worst-case for batter power, and range extender trailers are unlikely because EVs get progressively less efficient as the battery capacity increases (increasing battery capacity increases the weight). When you're starting with something as heavy as an electric RV, attaching even more weight seems unlikely to pay off.
(Now I'm curious if the relationship between range and battery capacity is merely sublinear or if it actually peaks at some point i.e. there is a maximum theoretical range beyond which increasing battery capacity reduces range)
The important thing to take away from this is we are still figuring out details and so should not lockin yet.