My old acrylic cabin door had a gigantic crack down the middle of it and I needed to replace it. After some research I found a new one for $599.... Way too much!!! After contacting a couple of plastic places and getting some rediculous prices for one to be made, I decided to make one. I bought a piece of black king starboard and got to work. I removed all the hardware from old door and double-sided taped it to the king starboard. Made a rough cut around the outside perimeter with a jigsaw then put it on the router table with a flush-trim router bit. After I had my exact copy I drilled through the existing holes of the OLD door into the new door(exact hole placement for hinges, latches, etc). I separated the two doors and removed all the double-sided tape. Next I used a "round-over" bit to round out the edges of the door and had to make a few cuts where the lock mechanism fits... A little filing to the lock mech area and VOILA, new door!!!
I bought it off ebay, not sure if it was XL or regular.... It is 3/8" thick. I would have went with a thicker piece but then the lock mechanism would not have fit.
I recently had the same issue with my door. Its cracked all the way down and I was going to replace it using the method you did. Do you recall the dimensions of the board?
I saw a video on a 1996 Maxum 2400 SCR and the guy stated, " 3/8'' x 24'' x 56''
Does that seem about right?