If I were going to make it from a box mix, I would use DH carrot cake mix and add each box:
1 cup flour
1 cup sugar
1 cup sour cream
1 box vanilla pudding
reduce your water slightly and add a little pineapple and a little fresh grated carrot
But anytime you alter a recipe you take the risk of a cake failer. Baking is a fine science of dry to wet ingredients.
There are a lot of scratch recipes right here in the recipe section of CC for carrot cakes. You could try mine if you like:
I prefer just boiling a can of Carnation evaporated milk for 2 hours for the caramel topping though. Just make sure if you do this that you do it ahead of time and let it remain in the water until it is completely cool. DO NOT try to open the can or even remove it from the water until it is completely cool.