I have had beach wheel's for years so my trailer hasn't got wet in years.. but when it did.. i would back it ONLY to where the trailer tire was 1/2 way in. i would then push the cat off (till it was balanced on the rear rollers) and let gravity take over... i would be sure the bows gently rode over the rollers.. it worked fine.

If you are submerging your trailer up the boat sterns in salt water... you will be reducing the life of your lights / trailer bearings / leaf springs / and everything else that gets wet (IMHO)