I have a box of Duncan Hines fudge marble cake mix, will it be strong enough to hold up to marshmallow fondant? or do I need to doctor it?
Also will it be ok to stack it? a 6 inch on a 9 inch
will I need dowels? (I hope not =S )
Baking stores are a little pricey here, no walmart to run to.

Thanks for any help and advice!

You should always use dowels (or some sort of support system) when stacking a cake.

if you're only doing one layer of 9" and one layer of 6" (each layer being 2" high) then you don't need dowels. if you're making two layers of each size for a tier (so you have 2-9" cakes stacked on top of eachother to be 4") then yes you need dowels.

The rule of thumb is dowels for every 4" vertical inches of cake.

This is a tutorial on stacking cakes. I've watched it over and over again and found little tricks along the way.

Your cake mix should be strong enough for stacking, but I am always one to err to the side of caution, and put in too much support, rather then little or none.
I'd rather be certain that the cake will stand.

Good Luck!

While I haven't made a ton of fondant covered cakes,, the ones I have made were all from a mix and they held up fine. Of course I roll my fondant really thin (because I hate the play-doh look of thick fondant).

Oki thanks, yes its only one layer of each cake and they are about 2 1/2 inches high.
Any advice on the cake mix?

Thank you everyone, your advice has been very helpfull!
Cannot wait to try doing this cake this week.