This is the 1000W board I designed on EasyEDA. It uses 20 MOSFETs, and don't forget the heatsink. Remember to tin the exposed traces with plenty of solder. Also, solder all the components except the headers, electrolytic capacitors, filter capacitor and the trimpot on both sides of the PCB. Also, use 1mm bare copper wire for the high-power vias. Now, don't solder the filter capacitor on the board, solder it on a seperate breakout board and connect the high voltage side of the transformer to the capacitor. The third breakout board is for the discharging of the filter capacitor. Just plug it into the inverter and it will discharge the filter capacitor.