While towing a 5000lb camper to go camping, the vehicle spontaneously started fire. When I exited the vehicle I noticed smoke and flames coming from underneath the cab. I opened the hood and it appeared that the fire was coming from the transmission area. Attempts we're made to extinguish the fire while awaiting the arrival of the fire dept. Attempts by myself, and others were unsuccessful causing the fire to burn through the firewall and into the cab. I was in a rural area so it took approx. 15-20 minutes for the fire dept to arrive. The fire eventually burned through the dash and the front windshield. Fire dept arrived and were able to put out the fire. Needless to say the vehicle was totalled.