If this cabinet has sentimental value to you, keep in mind that reptile enclosures have a finite lifespan, and you're probably going to end up throwing it away a lot sooner if you turn it into a snake cage, unless you really go nuts making it waterproof etc (very generous on the sealant). Your vinyl is a guaranteed way to destroy it nice and quickly.
You seem determined to avoid doing anything quick, easy, cheap and practical and using overthinking to find ways to make life difficult and dysfunctional. If you want to use this cabinet as a snake unit and not destroy it, just deck it out with the extra panels required, seal it with several coats of sealant (be very generous with the sealant or your cabinet will get soaked and rot - water or worse still urine/faeces is a great option for destroying wooden furniture) and add your desired electrical fittings.
You seem determined to avoid doing anything quick, easy, cheap and practical and using overthinking to find ways to make life difficult and dysfunctional. If you want to use this cabinet as a snake unit and not destroy it, just deck it out with the extra panels required, seal it with several coats of sealant (be very generous with the sealant or your cabinet will get soaked and rot - water or worse still urine/faeces is a great option for destroying wooden furniture) and add your desired electrical fittings.