The pilot reported that after landing on a trailer landing pad for the purpose of hot refueling and loading chemical product onboard, on completing those actions, the helicopter slid backwards off the trailer impacting the ground. The helicopter sustained substantial damage to the fuselage and tail boom. The pilot reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operations. The operator reported that the helicopter’s center of gravity required that both skid cross tubes be positioned over the landing pad, which required the front cross tube to be placed precisely near the front of the landing pad. The ground crew and pilot were unsure of the helicopter’s position when it landed but recognized that it was possibly too far aft. Following the accident, the operator installed extensions to the landing pad to provide a larger landing area for the helicopter.