Can I frost a styrophoam tier that will be the middle tier for a 3 tier cake with IMBC icing???? do I need to cover it in fondant first.. the cake will not be finished with fondant.. IMBC only.. but will it stand up indoors with 100 people in a firehall... not sur eif it is air conditioned>??

just go ahead and cover as you would your regular cake. If you are looking to reuse the dummy, then you would want to cover it with saran wrap 1st. Glad press and seal is good for this

well, frankly if the icing is going to melt off the cake it really won't matter if the cake is real or fake. It will melt if its too hot and with no AC depending on where you are located you might be okay you might not. But it shouldn't react noticeably different whether its on cake or stryo.

Great!! Thank you! I was doing the dummy cake to make things easier.. I neve reven considered this as an issue until now.. so I am happy to not have anything more to stress about, and just look forward to the trip, wedding and cake!!

Thank you for your help

IMBC will fall off your cake at that temperature (dummy or not). I've heard of people subbing half Crisco into their IMBC when they use it on cakes at that temperature (Crisco has a higher melting point than butter). Or I think somebody on here uses Smart Balance for all the butter.

Fondant will be perfectly fine (in fact, some people will only offer that in hot weather since BC can be so finnicky). My guess is you should be okay. I really don't know why the reception would not be A/C. But be sure you keep your cake as cold as possible in the house and freeze yourself out while transporting. Honestly, I'd be more concerned of decorations falling off the cake (borders, I've had that happen before).

Here's the info on Smart Balance. The crisco will simply make it a bit more stable.
http://www.smartbalance.com/BlendsFamily.aspx