If you are having trouble getting the warming rack for your Spirit II model to fit properly, chances are you may be trying to install it incorrectly.
There are 3 sets of slots along the left and right edges of the cookbox.
The set of slots closest to the front of the cookbox are designed for the optional rotisserie accessory.
The 2 sets of slots closer to the back are designed for the warming rack.
Make sure that you're using the 2 back sets of slots, and not using the rotisserie slots.