If you think you need 1000w you need Double that. When that heater and fridge kick on and run at the same time they will cause a strain on the system. Possibly pop a breaker/overload your generator. There is a difference between max and running watts. If your system can handle more wattage it...
Buy the best one you can afford and bolt it down to the concrete with anchors or bolt it to the floor. Even a thousand pound safe can be moved by a couple people using cut broom handles to roll it out and flipped on its back into the bed of a truck quicker than you expect