Tile

Not even tile will go over decking. Either the room needs to be rebuilt properly to interior construction standards, or you're basically left with using indoor outdoor carpet. And that done more as a rug than a glue down install.

Thank you all for your responses.
Glennsfc how thick was the AC exterior plywood you used?

Thanks again

I didn't install the plywood, so I don't know the actual thickness, but I assume it was 5/8" or thereabouts. Combined with the 5/4" base, it made for a very sturdy substrate.

I went out on a limb on that job, as it was for family, and I was praying it would work and be fine in the long run. It was and I was pleased with the result and performance.

A 7/16" exterior glue plywood is as thin as I'd go in such an application. 5/8" (9/16") is better. And secure fastening with proper fasteners is essential.

Vinyl expands and contracts so much with the heat/cool cycle that I would be very concerned about putting it in a room that experiences actual winter cold. What epoxy glue did you use glenn? And have you seen it during the depths of winter to assess the gaps then?

I used Toli LVT tile and used their epoxy adhesive. The tile hasn't shrunk, peaked or done anything in the time it has been down. My brother tells me that there are no seasonal changes to it at all. Of course, Toli is a commercial grade product and not your run of the mill consumer grade material.