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You mention that you've read the guide, but you don't specify which guide. According to the wiki page on Morvario's Base:
https://runescape.wiki/w/Movario%27s_base#The_storage_room
"When leaving, players must leave by the study's door. But it's not possible to exit the base, if the player's weight is 0 kg or less.
Players will thus need to do the weight puzzle or just force the door and take the damage from the trap. For players who can take the damage, forcing the door is the quick way out."
There are additional instructions on that page for doing the weight puzzle.