I put the insulation on three out of the four sides of the tank and then cut out a piece to lay over the top with a circle cut out for my heat lamp. The temperature increased--only now the temp is about the same on both the warm side and the ambient side (about 80 degrees). I'm hoping overnight the warm side will increase a bit more or I'll be in the market for a little space heater.

I did end up using tape. Honestly I'm not too concerned with the aesthetic of everything as long as my bp is warm enough.