Tiramisu mixture not firm I have tried to make Tiramisu chocolate mousse from this video many times. The chocolate mixture turns out great. With the egg yolks I add grape juice instead of wine and soft cheese instead of marcarponi - which seems to turn out great as well. 

What I fail to make is the whipped creme. I use Dano sterilized creme that is modified with vegetable oil (so it says on the can), fat 23%, made from skimmed cows milk and it says the milk fat is replaced by veg fat. I put the bowl and the whisk in the refrigerator, as well as the creme, but when I whisk it, it becomes more watery than fluffy. 

So today I got Fostered Clark's Powder Whip Wonder Whip Topping; that turned out nice and frothy, but when I combined it with the chocolate-egg mixture, it did not turn out to be the way it looks in the video. I had to put it into the refrigerator so the mixture became a little more firm; I could barely hold a shape in the martini glasses. 

What am I doing wrong?
If you are insistent upon substituting something for the cream, you are probably going to need to experiment with adding some soy lecithin (to make sure that the substitute fats don't separate), maybe some cold-soluble gelatin too for added stabilization (regular gelatin that has been bloomed and added when the mixture is hot might also work), and possibly a few other gelling or thickening agents.