The only thing I can think of is either that custom textures have been broken for a while and nobody's noticed (50% chance, the devs and the community are a bunch of doofuses sometimes) or that you're trying to do this on the PAL (European) version, in which case you need simply rename the folder to GMSP01.
<@skid_au> fishing resort is still broken: http://i.imgur.com/dvPiQKg.png
<@neobrain> dafuq
<+JMC47> no dude, you're just holding the postcard upside down
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<@Lioncash> pauldachz in charge of shitposting :^)
<@neobrain> dafuq
<+JMC47> no dude, you're just holding the postcard upside down
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<@Lioncash> pauldachz in charge of shitposting :^)