Labs_underpass_p.upk Instant
No, you can ignore the universal Mods.upk file for this method.
It allows for storing assets inside your level package, essential for functioning with the Rocket League Workshop.
Ultimate Guide to Custom Maps in Rocket League: Mastering Labs_Underpass_P.upk Labs_Underpass_P.upk
Create a backup of the original Labs_Underpass_P.upk to avoid losing the default map.
This guide will walk you through setting up, testing, and managing custom maps using the Labs_Underpass_P.upk file method. What is Labs_Underpass_P.upk? No, you can ignore the universal Mods
Take the custom .upk file you downloaded and rename it exactly: Labs_Underpass_P.upk .
Find your Rocket League map folder, usually located here: Documents\My Games\RocketLeague\TAGame\CookedPCConsole\mods Labs_Underpass_P.upk
You can directly create or import meshes and textures inside your level package.