Osso,I never advocate the use of 220s on beaver,If you do not get them to enter correctly --you end up with an educated beaver.
When I trap beaver in states that require total submersion of the 330,I make my castor mound,dig an area out in front until the water covers the top of the trap. I then use 2 cross sticks over the top of the trap,and block off the sides.Also I place the trigger on the bottom.
Does your 220 also have to be submerged totally?If you cant come up with a 330 ,and are forced to a 220---look for a pinch point to make your set. Tom