I have a Blue Ridge Spa by Jacuzzi, circa 2000 or 2001. It came with the house when I bought it about 15 years ago.

It was originally on a cement slab to the side of the deck, and since then I rebuilt the deck to recess it. Photo below.

It originally had a 2x3 border (with 1" of it showing), and underneath that was a thin frame (maybe 1/4") to make it pretty. Inside of that frame was a piece of Styrofoam, maybe 1/2" thick. Over the years, though, that 2x3 had almost entirely rotted away, and half of the frame was rotted and falling apart. So for the last several weeks I've busted out the old border, ripped out the thin frame, and replaced the border with a 2x6... the photo below shows the new border, and I left 5" out so it could be used to sit wine glasses on.

Underneath the deck, though, is where I have a question.

The front of the hot tub (where you see the orange tag in right side of the photo) has been more or less exposed for the last 10 years, when I began replacing pumps and other hardware; I had to break it off to get to the heat pump, and after that I just leaned it back in place. It never had Styrofoam or anything, so the only insulation was the foam that's adhered to the acrylic shell. The front is easy-access to the main circuit board, heat pump, and circulation pump.

To the back-right is the jet pump.

Back-middle, there's some sort of PVC junction that appears to be attached to the thin frame. That's the only part I couldn't get out, when I pulled on the frame all of this PVC started to come with it.

On the left, there's nothing but tubes.

I don't want to leave all of this exposed, so I was planning to staple a sheet of plastic to the bottom of the deck and let it drape down. Maybe lay 2x4s around the cement slab underneath, then staple the plastic to that, too... then it would be nice and stable, but easily moved when I need access.

Question 1: is that OK to do, or would it cause condensation inside that might be a problem for the pumps and circuit board?

Question 2: I'm in zone 7A, so sub-freezing temperatures aren't uncommon during the winter. Would you recommend any type of additional insulation around the shell? I thought about regular pink home insulation, tucked in between the pumps and the shell, but I wanted to run it by you guys and gals first.