Sorta Handyman - Sealing Out Cold Air

This past weekend I did some handyman work at home. Our apartment is always slightly colder than it should be, even though the sliding glass doors and windows are double paned. We realized that it was because a good chunk of warm air was escaping beneath the door.
Even though the door had a gray rubber liner beneath it, there was still a gap. This let warm air out, cold air in and a dangerous entryway for spiders. We had to figure out a way to plug up this gap beneath the door. How were we going to do it?
We had purchased one of those things from Bed, Bath & Beyond that would fix this issue. The problem was that the sealant part of the device was actually too high above the floor when the door was closed. What this ultimately meant was that it didn't do anything. The "air sealing" section wasn't covering the gap. It just sat above it, letting spiders in and keeping the warm air filtering out. How was I going to seal this gap?
That's right! Craft foam! I cut pieces of craft foam, hot glued them together and then hot glued them to the metal door frame. Hot glue worked well because it wouldn't leave a permanent mark on the frame. Now the rubber liner had something to close against and it was completely flush.
So, that was my handyman work I did last weekend. We have warm air staying in, cold air staying out and the remaining spider colony being eaten by the cats. Overall, the project took 15 minutes and cost around $3 (I already have craft foam and hot glue laying around).