We had a contractor add a sunroom on the back of our house and we said we would install the finished flooring. We have a bunch of lay flat vinyl floor planks and I'm wondering what we need to do to prepare the subfloor for installation. It is the standard interlocking 3/4" subfloor, nothing fancy. My question. Do I need to prepare the surface in any way prior to install of the lay flat vinyl planks? I'm thinking about using something to fill in the gaps, where the floor seams aren't totally tight. I was also considering applying a layer of Redgard on top of the subfloor before installing the floor, but didn't know if that was overkill. The room does not tie into the house HVAC. Appreciate the help.