To attach the sucker, first you have to drill two hole which is slightly smaller than the head of the sucker, force it through and then use something to hold it in position (prevent it from falling off). see picture
Brine shrimp when frozen will float. Basic rule is to keep your trap away from direct current, push it into the furthest concer away from the door, without current disturbance even if it melts, it will just settle at the bottom of the tank and not drift out.