@Abby126,
A two hour drive and display time in the summer heat and humidity will not work for this type of cake. The type of cake has to be appropriate for conditions.
All whipped cream, whether stabilized or not will deteriorate when exposed to heat and humidity. Stabilization simply slows the deterioration process over 24 hours of refrigeration. Stabilizing the whipped cream is not a substitution for refrigeration.
The addition of fresh strawberries potentially increases the rate of destabilization due to the natural water in the strawberries.
Sugar is hygroscopic, meaning it pulls water from its environment. The sugar in the whipped cream and cake will pull water out of the berries. If the whipped cream is exposed to air, the sugar will also pull moisture from the humidity in the air. You can see sugar’s hygroscopic properties by mixing a bit of sugar with berries and let it sit. In about 30 minutes there will be a lot of liquid in the bowl and the berries will be soft. That's what is going to happen when you put the fresh strawberries in the whipped cream.
It’s impossible to know how long a whipped cream and berry filled cake will hold up. To be honest, the transportation time and weather conditions are such that most experienced cake bakers would not agree to bake such a cake.
I really encourage you to bake a test cake very similar to the cake as ordered. Then box the cake and place the box outside for the time you allocated for transportation. After the estimated transport time, remove the cake from the box and leave it outside for the amount of time you anticipate the cake to be on display. If the cake is still intact—and it may not be, slice it to check the quality of the IMBC and filling. A cake sitting in warm and humid conditions might look intact, by the icing and filling may not be edible. A real buttercream that sits in hot humid conditions will be very greasy as the emulsion begins to break down. Also, if the IMBC begins to break down, any moisture it releases from the butter will start to disintegrate the fondant. Similarly, a heat sensitive filling like whipped cream and fresh berries will become runny if it sits at room temperature or higher for too long.
I know baking a test cake is a lot of work, but if you decide to proceed with this cake, it is the only way to get a rough estimate of the tolerance range of the components and an estimate of your window of time for getting the cake delivered and served.
Given the components, there’s another important issue that should be addressed: food poisoning. The government uses water activity level to establish food storage requirements to guard against food poisoning. Foods with high water activity levels must be stored at or below 40°F or at or above 140°F. The longest food can safely consumed after sitting at room temperature is 2 hours. But that 2 hour window is just a guideline.
Three major components in this cake, IMBC, fresh fruit and whipped cream all have extremely high water activity levels. In addition, water activity increases with temperature. This cake will be exposed to conditions above room temperature, so that increases the potential for rapid bacteria development. In the presence of water and the right temperatures harmful bacteria can double in number in about 20 minutes.
The water activity level of these three components is so high, that every state with cottage food laws prohibits the sale of baked goods made with these components. The rational is a home based business does not have the mobile refrigeration equipment necessary to safely transport and store high water activity food on site. I know this is not a commercial transaction, so does not fall under these restrictions. I just mention it so you have some frame of reference as to the potential health risks involved with this cake and the conditions you are up against.
The baker is responsible for food safety during the production, transportation, and delivery of the cake. Once the cake has been delivered, the customer is responsibility for the condition of the cake at delivery and thereafter, including proper storage of the cake to guard against food poisoning. Even in a non-commercial transaction, its advisable to disclose and discuss the food safety issues with the bride and groom to ensure every one understands the risks and is in agreement on how the cake will be handled to guard against food poisoning.
A bride may request any cake she desires, but it’s the responsibility of the baker to know what is possible, what the risks are given the cake components and the environmental conditions, and advise the bride accordingly.
One of the most difficult lessons in baking for others is learning how to say No. I have to say No a lot, and it I still feel bad when I do.
I do not in any way mean to sound critical or discourage you from baking this cake. My intent is to bring the baking and non-baking issues to light so your cake is successful and the experience is a memorable one for all involved. Most baking resources address the baking, with nary a word about the important non-baking issues involved in creating baked goods for an event.