You truly are an artist!! In today's tech world most would snap a pic, you drew it out. I honestly love that!!!! Keep the arts alive!!!
I think your best bet is adding a "scab" to the wall where the gap is. Get a piece of 3'4" scrap (Home Depot or Lowes often have some pieces kicking around) or something like it, maybe some "finish trim". I would bring the pic with you and they will most likely just get you what you need. Bring the measurements and they will probably cut it to fit for you. Then simply fasten it to the inside of the enclosure to block the gap. Liquid nail or hot glue and a few bolts/washers. Just choose the right length and finish to avoid any rough edges exposed to your snake. Using a few "L brackets" will tighten the enclosure up and prevent further movement, spreading gaps, etc...