I live in a very cold victorian house and need to keep my hingeback tortoises warm enough through winter - with all the heating in the world, the air will still be too cold. Vivariums are too expensive for me, so i want to cover the top of their wooden tables with some clear sort of plastic to keep the heat in. The actual bulbs are inside the walls of the table and will be fixed to wood, not near enough the plastic to be an issue. I am wondering which product will be best to keep the heat in enough to not be an issue, be hard wearing or cheap enough to replace, and allow me to still see them. My main options at the moment are: Clear PVCu Corrugated Sheets, Polycarbonate twinwall sheets (4mm) or an acryclic sheet (expensive though). Which would be best? Or are there any other ways to keep the heat in? 
