I wouldn't worry about the durability of them. Still haven't seen any of the rubber, o-rings, seals, gaskets, plugs, etc. fail or show any sign of aging/corrosion/lack of staying power. To include the K-7 and battery grip seen in this video (the K-5 I no longer have for unrelated reasons).
And that was two years ago - I've had MANY "WR" incidents lately, including a 4 hour photoshoot
yesterday. Here's a teaser image from an animated .gif I made for the upcoming 18-135 WR review here on PF. For the full animation you'll have to wait until the review
Don't worry about it, however do make sure that you close the flaps deliberately each time. Or just get a card reader - you can get them cheap on eBay for literally $5 including shipping.
-Heie