heating small spaces with minimal electricity

so, i need some creative help here... i have a bit of a problem.
here it is.
as winter gets closer, its getting much much colder outside, and me and some of my friends have this activity that really enjoy, its best done outside, or when no one is home. we really like playing our guitars/tubas/saxs and smoking hookah. normally we'll just go to random parks or open spaces and have some hookah and jam for a while, but like i mentioned above, its getting cold outside...
so heres our idea, i need your guys help making it work.
i drive a pickup truck, and i have a shell/topper for my pickup truck.
viola, we have an indoor space for our activities.

Problem A: its still cold out side, and the bed of a truck isnt very warm, even with a topper
Problem B: how could i get electricity in the back of my truck?
Problem C: i only have about 80$ to send on this....

so far the best thing i can think of is to get a ciggerette plug adapter for a normal plug and plug in a space heater and just run the cord thourgh the car window and the shell window, but i dont want my cars battery to die!
so, any one have any ideas?

 

http://www.roadtrucker.com/12-volt-heaters-blankets-sheets-1.htm


x

 

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Cost: $59

 

LOL



I like this deal:



The Kandle Heeter Candle Holder is priced at $25.95 and available from the manufacturer at www.heatstick.com.

or you can make your own candle heater

 

ive been thinking about getting a small propane heater..

 

You could use a propane heater-but be very careful. It is using up all of the oxygen around you.

Check out this heater-

http://www.amazon.com/Coleman-5053A751-Perfectemp-Instastart-Technology/dp/B0009PURYU

 

well so far, weve found that 4 people sitting in a small space heat it up pretty freaking quick, so do hot charcoals on the hookah

 

dude how are you gonna put a tuba in a pickup truck?
whoooosh

 

Insulate the canopy.