What is an easy way to turn a heavy-ish cake?
Well, the obvious answer is to buy a metal cake pan. Otherwise:


You could try putting a jellyroll or cookie sheet under it. Then grab the cookie sheet to rotate. Beware that depending on what the pan is made of, it may affect browning especially on the bottom of the cake. Adding some insulation (e.g., parchment) may help.
Plain aluminum foil may work too. That'll slide fairly easily on the rack, and again you can grab it easily. Especially if you pull the pan out of the oven, aluminum foil surrounded by air will cool quickly, and you'll be able to grab it without the inflexible mitts. 
Similarly, a sheet of parchment paper under the pan. Same principle as the aluminum, except even at oven temperatures you can grab parchment briefly.