Postscript
A few days later, I started re-assembling the hot tub.
In searching for the leak, we had removed approximately 9 cubic feet of insulative spray foam. Now I had to replace it. I briefly considered buying a crate of cans of spray foam, but the cost seemed prohibitive. Anyways, I believe Dimension One chose to use spray foam for its ease of construction, not its superior insulative ability (and certainly not for its maintainability). Instead, I made a trip to House of Foam in Palo Alto. After explaining my situation, House of Foam gave me three options:
- buy new foam: $65 (who knew foam was so expensive?!)
- pull pieces out of the leftover foam bin, at $1/piece.
- buy 3 of their pre-loved foam cushions, the kind you find inside your sofa cushions: $3
Slicing the cushions to fit the voids in the hot tub was a bit challenging. After some pointless hacksawing, I found that scoring the foam with a utility knife, followed by manual, hulk-like ripping, proved most effective.
Once the foam was in place, I replaced the siding. I repaired the broken siding with Liquid Nails, fitting the pieces together like a jigsaw puzzle and clamping them to dry. Based on Clyde recommendation, I used stainless steel wood screws and a countersink drill bit to reattach the siding. In the process of removing the siding, I had damaged the waterproofing shiplap structure, so I attached a waterproof barrier between the siding and the foam (improvised from an old plastic tarp).
Now I'm enjoying my hot tub immensely!
Thanks, Clyde!