greenhouse Budget greenhouse with budget heating question

Hi guys, 
I'm a small-time grower with a growing passion. I'm still young and can't spend a lot of money on high-end equipment. Therefore I like to use as many low cost solutions as I can. Recently, to elongate my season a little and for the experience, I bought a plastic greenhouse. It's about 50 x 70 x 170 cm. The plastic seems to be of good quality but I have no real knowledge on that subject. 
Now the night temps are dropping to 10 degrees Celsius here and I would like to keep the temps up a bit. I've read that putting a bucket of water inside will help regulate both day and night temps. I've also got a heating mat with temperature regulator, which turns it on and off at the temps I set. Is it worth it to try to use this to heat up my greenhouse at night, or do those heating mats not give off enough heat?
Hey dude, I found a small panelheater works mint.
Here is my setup as it was about a year ago, I'm still using the same heater, just bubblewrapped the greenhouse. Cheap as, and it works pretty well.