I have used Exo Terra Desert Heat Wave mats on my Vision enclosures for years with no problem (hooked up to a good thermostat). I'm switching to pro products heat panels as soon as they arrive... maybe today! Why can you no longer do heat panels with your 221 enclosures? I have one and don't see any reason you couldn't mount a small heat panel in it. Also, depending on where you live, I don't need my 221 anymore.

For the 221's you don't need the $16 lock. That one is only necessary for vision enclosures with a center support behind the glass. You can use a regular old display case lock, which should be under $10 at a home improvement store.