Having seen everybody cut the slots with drills I thought there has got to be an easier and quicker way. There is! I used one of the small cut off tools, around £35, they are designed to trim door trims when fitting wood flooring.
I was going to place a thin piece of alloy under the blade so as not to damage the bonnet, this was not needed, the teeth are all on the top of the blade so I just rested it on the bonnet itself and no damage was done.
Use it as a plunge cutter, the blade is wide and thick enough so it doesn't flex giving a straight cut. For the top cut I just cut from the inside of the bonnet.
You can see from the top cut that the thickness of the layup of the GRP varies, this is quite normal.
I then swapped to a smaller blade for the vertical cuts, this blade was a bit too wide so I made the cuts at an angle to take out as much material as possible.
I then took out the excess material with an air die grinder and then ran it along the inside edges to get them roughly straight.
Finished result, only took 20 minutes from start to finish, obviously it will need final finishing. I haven't fitted a grill, it is just the patio table I was working on. I wonder if she would notice a small bit missing?
I would like to try and run the lower section of the opening into the opening about 25mm, I think it would neaten it up but will cause quite a bit more work.
I will be using the same method for the slots in the wings although I have bought some alloy finishers so they will hide any bodgery in cutting the slots.