So if you throw a nade at it theres definitely an invisible wall there

Maybe unlock the entire Easter egg, including the ending, but before going into the truck, use the launchpad and see if you can get into that room.

Just FIGURED IT OUT. It will unlock when you get the "mystery" powerup that is shaped like 2 knifes, I have no idea what else is unlocked when this happens, but the barrier to the room dissappears. You need to purchase the double jump perk or get it through the rainbow perkaholic easter egg, and activaste the spring trap. If you hit the spring trap from the church side, line it up with the window, and double jump at the right moment before you hit the wall, you should be able to crouch and enter the room. MAKE SURE YOU HAVE THE MYSTERY POWERUP, it only lasts like 15 seconds which is enough time to activate the trap and retry once if you miss the jump. Inside youll find the raygun 2.5 and a buyable assault rifle, nothing else.

Inside, there is the Raymors wonderweapon and two regular looking AR's on the left wall and then 3 of the special color AR's on the right wall

you can hide up there indefinitely, but there is an invisible barrier that you cannot shoot anything past (or grenade, etc)