The aluminum tape inside the cardboard tubes was my idea and my bulbs have not melted the plastic. Others have said that their lenses melted.
LINK HERE
Painting the interior of the tube gloss white will help transmit light better. Using aluminum tape on only half the tube (nearest the bulb) may help reduce heat too.
Drilling a few holes or slits along the length of the tube can also allow heat to escape.
LED bulbs won’t dim but would produce less heat.