Here`s the PCB "proposal", I hope that it`ll works without (capacitive/oscillations) problems. I didn`t try it, so far :-).
See that "stopper" resistors R2 & R4 must be mounted with it`s "body" close to the G-pin, "upward". Fix the heatsink somehow (little screws left and right through the board, or...?).
Without "proper", photo process it can be made with nail-polish, then Fe-III-chlorid. Be carefull, good luck!

• DN2540 CCS cascode schematic