Monitoring the parameters inside enclosed metal vessels or thick concrete walls as found in dry storage canisters and nuclear reactor vessels is crucial to ensuring safe reactor operation and fuel security. In this paper, two energy harvesters, namely the gamma radiation energy harvester and the thermal energy harvester, were built to power the wireless through-wall and communications for in-situ monitoring of interior conditions in nuclear canisters. The gamma radiation energy harvester was found to have an energy output of 17.8 mW during the first-year canister storage. However, this energy harvester was burdensome, and the performance deteriorates rapidly with time. The thermal energy harvester was thought to be a more practical solution. The power output of the energy harvester was about 93.9 mW in simulation and 46.3 mW in the experiment after 50-years storage in the canister. The power output of this energy harvester can be further scaled by adding TEGs at the cost of larger size.