vinyl over concrete/wood Help!

Ok, here's the situation. I am in the midst of a bathroom remodel. Removed the old ceramic tiles, to find a concrete bed over the shiplap subfloor. The concrete is about 2" thick. also, where the vanity was, there was no concrete, so there was a 2" depression in the vanity area. I filled the vanity area with 3 pieces of 3/4 osb. I was going to install a fiberock or plywood underlayment over top of this with underlayment construction adhesive, but I seem to see from the many posts here that underlayments over concrete are a bad combo. I will be installing sheet vinyl flooring. I guess my question is do I just get a big bag of floor leveling compound and pour it on? I have had pretty bad luck in the past getting leveling compound smooth. What is the best way to go about this? any and all help, instruction would be greatly appreciated. I am supposed to be laying the floor tomorrow (Thurs) so if you have any ideas, please post them asap. Thanks!

Yours in frustration/desparation

Greg

 

I'd have to see it in person to give a good consultation.