I have an order for a wedding cake with Fleur Di Lis on the sides and a large one for the topper. My plan was to use fondant and a silicon mold to make them. I would attach the small FDL's to the sides using royal icing. My idea for the topper would be to make 2 FDL's then attach them back to back with a dowl rod between the two to insert into the cake. But, the more I think about it...would the solid fondant shapes be too heavy? I was thinking of using the mold with rice crispy treats then covering in fondant.

I'm new to using fondant molds & rice crispy treats. I'm open to all suggestions!

The fondant won't be too heavy if it's not too thick.

No it won't be too heavy. Go for it

Be careful with rice crispy treats they can be heavier than you think. The first time I used them as a sculpted topper I thought they would be light as air, they ended up squishing the cake. I'd do a test run if you intent to use snap crackle and pop.

I guess it would depend on how big the topper would be but generally, fondant figures and such are really not that heavy.

I made this "40" topper and worried that it would be too heavy but it wasn't.

http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1323390

It was a good 4" tall and was just fine. I didn't even use dowels underneath.

But as KawaiiCakeCook pointed out, you could always test it. HTH.