ummm, one trick you might want to do is to only put the hoses on the nipple partway, then when you squish the "hat" on, it pushes the hose all the way on with no fuss. Also, if the hose has been on the nipple before, you might want to trim the old, stretched section to make it fit tighter onto the nipple...or spend a few pennies and buy a whole new section of LP hose, maybe yours was a little larger than normal?
Ray