Mr Siddons, from Madora Bay, has banked more than $15,000 since he started raising money for the cause less than a decade ago.
But this year he used his exposed booty to boost his fundraising.
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READ NOW“I’ve jumped before, so I was ready for that rush but the mankini made it that much more… crazy,” he said.
“It was below zero when we left the plane, so it was pretty cold and it’s hard to breathe with all that air rushing past you but apart from that, it was just the exciting rush that I got the first two times, with a little less fear.”
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Mr Siddons said he collected donations of $3281 this year, which is a personal fundraising record.
“It’s not the first time someone’s jumped in a mankini, apparently,” he said.
“The whole crew were very supportive and encouraging.”
Mr Siddons said photos of the jump were popular with friends.
“Everyone is saying stuff like ‘legend’ or ‘Where was the warning before that photo went up?’ and ‘Did they burn the harness afterwards?’” he said. “All friendly banter but the majority is amazement, I guess.”