Dampen a rag in water. Wipe down the aluminum trailer's dent to get it moist.
Place a plunger against the dent and push down to create suction.
Pull back on the plunger to straighten the dent. This may require several attempts. If ineffective, continue to Step 4.
Place a can of compressed air on the ground in front of you. Have a rag handy before proceeding further.
Hold a heat gun about 4 inches away from the dent in the aluminum trailer. Put it on the highest setting, turn it on and wave it over the trailer dent.
Remove the heat gun and rapidly turn the compressed can of air upside down to make the carbon dioxide inside the can rush to the sprayer.
Spray the dent immediately to get the most carbon dioxide onto it. The combination of heat and carbon dioxide will cause the dent to pop out. If it does not pop out immediately, push the dent from the opposite side with a rag while the aluminum is still soft from being heated.