HELP FAST! Sealing mistake!

[pillywiggins1]

I need help figuring out how to fix a mistake on my DIY boa enclosure build. My hubby picked up an oil-based polyurethane for our massive plywood build by accident, and we got 3 coats already on by the time I caught the mistake. We've already sunk a good bit of cash into this build, I really do NOT want to start from scratch. What can we do to make this enclosure safe for our 9' red-tailed boa? Can we just go over it with several coats of water-based polyurethane, or do I need to get a VOC encapsulating sealer like AFM Safecoat Hard Seal? Do we have to sand all the old polyurethane off (just thinking of it makes my head hurt!)? Please help!