By my understanding the seller is violating eBay's rules. The attachment of the "Casita" name is nothing but a traffic lure. This is a PlayPac - nothing to do with a Casita shy of being a molded fiberglass trailer. Or in this case - a moldy fiberglass trailer.
I had a PlayPac once. The rotted floor near the door is no surprise. It's due to the design of the trailer. There's a glassed in well that runs the perimeter of the trailer. Any water intruding near the door goes down into this well and STAYS THERE. Instant recipe for rot. Could have been solved by putting some drain holes in the bottom - which any owner should do - but no.
PlayPac's are exceedingly rare. There were less than 100 made ever. I've only seen one that appeared to be stock. Every other one had been gutted and rebuilt inside. This one needs to be. The windows hinge at the top and tilt out. I could NOT make my front window watertight on the road. I eventually screwed it shut and caulked it in defeat. The bi side windows are just as bad - I replaced the side and rear windows with modern glass sliders. From what was left of the original interior in mine - I could tell the side windows had leaked too.
They came stock with a dome shaped bubble window in the top. Kinda cool - but if you're 6' that's the only place you can stand up.
I reworked mine to have a 2 person dinnette up front and a permanent queen bed (with a residential mattress) in the back. If I were to redo it - I'd go with a redo of something close to the original floorplan. Twin beds along the sides with a table at the back wall, privacy room in the front corner and "kitchen" under that front window.
The overall construction is fairly interesting - molded fiberglass with 1/4" pink foam insulation glassed in on the flat parts.
This seller is a very familiar reseller of fiberglass trailers. I don't know where he ends up gathering them up - but he must be picking them up somewhere regionally for quick resale on eBay. At most they're getting a quick scrubbing between.