Before you try anything make sure you get the motor dried out thoroughly and then make sure the battery is fully charged. The top will not lift without a good battery or with only the converter. Check all the other electrical connections to make sure they are clean and dry. Put the battery on charge at least overnight then remove the charge and allow the battery to sit several hours. If it is charged properly it should read at least 12.6 volts with any load. Hopefully the top will go up.
How did the motor get under water? There should be drain holes in the compartment. If not, make some. A half inch drill will work.
There is lots of info here on the forum about the lift system.
http://www.hilotrailerforum.com/f22/