Yep, it's a PITA for sure, but it fits. The trick is to keep it as even as possible as you pull the pack up around the foam from the bottom a very little at a time.
Or just do like I did and bust the dȧmn thing into pieces, it fits really easily then!
Good news, the top is much easier!
Patience my friend....
I had to put a bit of carpet tape on the top to keep it from falling out. As far as the bottom foam........I got help from a young gal. They are experts at getting into those tight jeans. It was done in just minutes.