Working on a job involving cut-out precision board letters installed on PVC. How do you recommend installing the letters?

This is for an indoor installation. The PVC sign will be installed onto a stone type wall (like a fireplace wall). Customer is doing that installation.

Foam letters will be primed and painted 1" thick. I was planning to leave the back unprimed for adhesive purposes. Will Liquid Nails work? Or do I need to maybe drill and put screws or something into them from the back?

Use silicone adhesive if you are going to leave the latters bare. Use V.H.B (very high bond) from 3M if you paint the backs.

Lay a pounce pattern down for your layout for letter placement.

The backs will need at least a prime coat. Use a small piece of VHB to hold the letters in place while the silicone dries.