all i do is use some 5 min epox to glue the firewall on, make sure u have a good bead all in all the corners

as fot eh collar, i had the same exact problem, the didnt really think their design through very well. all i did was drill the center hole out so the coolor went through. You dont however want to just take the collor off, because that is what is holding the motor together. With out it, the thrust of the prop will just pull the bell off of the arm.