I don't have a key for mine either. I use the 6" flexable ruler I keep in my pocket to open it. I can do it in the dark with my eyes closed in about a second or less. Just slip it in the crack centered above the lock and the door drops open.

Or, like said before, poke a hole in the cardboard and rech inside and unlatch it. what does new cardboard cost? And is yours any good to start with?

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-