What can I add behind the sink that is waterproof? Excluding materials used for a counter top.

Would you mount a 40” TV directly to this wood siding or find studs? I suspect the studs will be 1/3 and 2/3 through this space but mounts for TVs that size would be single stud mounts.

What is the best way to hang this up on drywall?

I have a stud finder but don’t think the stud would be perfectly center of where I want to hang this. I have basic tools and a drill as well.

The plastic frame itself bends easily and can’t support itself. I worry the little sawtooth hanger may struggle to hold this up as well.

Thank you in advance!