I am baking a sheet cake for a retirement party Wednesday. I am using 2 boxes vanilla cake mix in each of two 12 x 18 2" deep pans. For the filling I would like to use a thin layer of buttercream and then over that a jar of Smuckers Butterscotch Caramel topping before adding the second layer. Has anyone ever used the caramel topping Or will it run all over? Any help would be appreciated.

I have not used the caramel topping, but for "squishier" fillings, use a stiff buttercream to create a dam around the outer edge of the bottom layer.  Then make sure not to overfill with the topping.

There are many posts on CC and videos on YouTube about how to pipe the dam.

Yes thank you. I do intend on piping a dam and have also made a foam core cake board to hold the weight

You know I bought a jar of that a while back, on impulse, thought I'd drizzle it over cupcake icing swirls.  It was runny as could be.  Ended up throwing it out.  It had no viscosity.  It might work, it might just melt into the cake  ?????? IDK

perhaps mixing it in with the buttercream and decreasing some of the liquid would do the trick and still give the caramel flavor?