I used polycell active gel, I found it worked well to strip off the top layers then sanded down the rest which was quite easy. Seemed to work quite well. I used the angle grinder with a sanding disc to take out the crazing, I also used a belt sander with 60 grit as well to take out large panels of crazing. I found the power file very agressive and quite tricky to control to get something anywhere smooth. Then tissue up the crazed areas, smoothed, filled then a final coat of upol to get a smooth finish to send off for spraying
Dave