So, before the dash is in...
Did you have a generous piece of rope caulk around the shaft where it goes in the cowl? That is the most important part of getting them sealed. In my opinion the white foam 'gasket' is pretty much useless.
Not in the way of the dash going in at all as far as I can see. I got my kit from Schumacher and it came with butyl calk strips to seal the shaft on the inside but over the foam gaskets.