On a cake, if use whipped cream rathar than butter cream is it okay to put a ganache over it? because i know whipping cream doesnt do hold if temperature is humid and so im afraid its going to colapse if i pour over the chocolate ganache. is that possible? or do i have nothing to worry about? 

Ai don't think u will have any problems if you are only going to pour over the ganache....

ANo don't pour the ganache over whipped cream you will not have a good outcome.

Ayou will have to freeze the cake before pouring the ganache. the ganache should be warm and not hot. you will need to work quickly in order to avoid melting of cream.

what if i stabalize the whip cream? can that help? 

AI use whipped cream a lot in my cakes. Just add gelatin and let it set in the refrigerator for a few hours.