I dont like bilt hamber clay
what you can use for clay lube is your car shampoo mixed with water, about 20ml to 500ml of water, this what i use if i dont have any clay lube, another good clay and good value for money is the clean your car yellow clay, a really good clay, TBH the megs clay kits are very expensive for what you get, as for polishing in the rain, Why? like said above it will need to be buffed anyway