Hey, I'm working on Epic too.. I think we would be able to do it if we could download the maps. HOWEVER- at the time of making this comment, it appears that some maps won't download unless we launch the game from Steam- which is physically impossible.
If you were able to download it, you can manually add it in I think, which is a lengthy process, but can be followed but for now I think we're stuck bud.

Here's some more info I found, hope it helps!
https://www.reddit.com/r/RocketLeague/comments/iylotu/tutorial_how_to_play_workshop_maps_with_the_epic/

WHAT MAP IS IT

i wanna know how to download it