Keep temperature at exact 62C/143F for an hour
Are we talking liquid or solids? Water has a high specific heat, meaning you need a lot of energy to change their temperature. That being said, I'd either go for a sous-vide approach, seal whatever you want to keep at that temperature in bags and toss it into a pre-warmed 62° C water bath, or buy/rent a medium/upper quality range dehydrator. These usually work for temperatures between 50-90° C, and are quite accurate.