Anyone ever done real lemon curd in an outdoor wedding in July for 300 people? Cake will be in the shade with fondant on it, but still..I've never done a cake full of lemon curd.
It would be considered 'safe', but you will still want the cake and filling cold before it goes on display.
I personally don't like the thought of cooked eggs at summer temps even if there is a lot of sugar to "preserve" - recipes always say to refrigerate curds. I just needed a lemon curd-type filling that had to hold for two days unrefrigerated. I bought two sleeves of the lemon-flavored pastry filling and added lemon extract and fresh lemon juice - it was pretty tasty.
I have a sleeve of that lemon filling, and the bride tried it but wants it more "lemony", so maybe I'll do that, just to be safe...I don't feel good about curd outside in mid-July, and the m.o.b. is worried enough about the heat to have ordered fondant instead of IMBC, so I think we'll just stick with the premade filling.