I have an order for a hippo cake and I would like to make the water that he is in look realistic. I have read posts about using piping gel but my concern is that the cake needs to be delivered on Thursday and has a 5 hour journey to the venue and the party is only on Saturday. I will be doing the water effect on wednesday. Will the piping gell still look alright by then?

It is probably too late to be of use to you, but when I use it to coat 'eyeballs', it keeps it's shine for quite a long time.