Okay, this is a totally random how-to...
I was dared to make this on a random drunk night with some friends... and she totally didn't remember even talking about this... hahaha. But we made it anyway... because I'm just like that!
Step 1: Get pick up truck.
Step 2: Tape tarp in place around bed of truck.
Step 3: Fill with water (I used two hoses from two spigots at my house)
Step 4: Get the water system working.
Tape hose to pump system (this is the fancy version)- we used a koy pond sized one. Retape a few times to make sure there's no leaks.
Step 5: Build fire-- this wasn't hot enough so we used the little camping grill I had lying around. We taped the hose to a copper pipe and sat the pipe directly above the fire, the idea was that the water would absorb heat through the pipe on the fire.
Step 6: Wait about 2 hours for heat to actually work. Now, if you have time in the morning, filling it early will allow the sun to help... I, on the other hand, woke up around 1-ish, so I missed prime sun heating time (10a-2p).
Step 7: Enjoy!