Been using these tidy little inserts I got from aliexpress lately and figured I’d take a few photos and share how I’ve been doing it!
Step 1: Drill the bolt holes through the enclosure. I use a 5mm bit as I want to use m5 enclosure screws. I keep it tight at this stage so that there is tolerance for it to open up a little for possible fitment issues later.
Step 2: Apply adhesive backed EVA foam as a gasket. I usually do a strip at each end first, overhang it and trim flush with the edge of the enclosure. Then I stick down the long runs, being careful to maintain a tight join with the first strips.
Step 3: Ensure that you have the deck/enclosure oriented correctly and gently but securely tape the enclosure down to the deck, without taping over any holes.
The gasket should help the enclosure to sit snugly with gentle pressure from the tape.
It is important that you don’t apply any significant pressure to the enclosure while pre-drilling. The enclosure needs to be sitting relaxed.
Step 4: Using the pre-drilled holes in the enclosure as a guide and the same 5mm bit, drill through just the surface of the deck. This will serve as a pilot for using a bigger bit in the next step.
If your deck has significant curvature, it makes for a neater installation if you angle your hole to be perpendicular to the surface of the deck. But drilling perpendicular to the deck surface can mess you up later if you end up needing a thicker gasket.
If you are concerned that your enclosure may be a tight fit or that you may eventually need a thicker gasket, i’d recommend having the deck secured on a level surface and drilling all the holes directly downwards.
Step 6: Choose the correct size drill bit for your inserts. The best way to decide what size to use is to do some test runs into similar material. I use scrap ply. The right size will be when it still takes significant effort to screw in the insert, but doesn’t deform the surface in any way.
Once you have determined the size, you need to determine the depth. I line the end of the insert up with the start of the drill bit and tape around it to mark the depth. Make sure your depth is not going to penetrate the top deck surface.
Step 7: Carefully drill your piloted holes to depth. The tape around the bit will be easily damaged by ejected material, so it’s important to back the drill off and let this stuff eject several times per hole.
It’s a risky way of doing it, as the drill could bite and just send through the deck, but if you’re confident with a drill and your deck is well secured you’ll be fine.
You could alternatively use some kind of depth stopper or similar, but tape works good for me.
Once the holes are drilled to depth, clean up the edges of the holes to remove any burrs. Make sure all the holes are free of debris.
Step 8: Glue up the holes. I use a cotton tip that i cut the end off to mix up the epoxy and then to spread it around the inside of the holes. You don’t want too much glue in the holes, just enough to coat the walls.
Step 9: Drive in the inserts. The double nut method is my favourite. As my inserts are M5, I use an m5 bolt with two nuts locked tightly against each other, leaving enough room for an insert to be securely threaded on.
It is important to leave thread above the nuts as well, as they may need to be loosened later.
I use a drill to drive in the insert, but you need to be very careful not to go too far. If you drive it in too far it will damage the top surface of your deck. I usually feather the trigger towards the end, while touching the top surface of the deck and feeling for any distortion there.
Once you have reached your desired depth with the insert you should be able to just back out the bolt. Sometimes the insert will want to come out with it as it has binded against the nuts.
If your insert is coming out with the bolt, you need to carefully get the insert back to depth and then use a spanner/s to lightly back off the 2 nuts and release the bind. Once released and the bolt removed, be sure to reseat the nuts.
Step 10: Clean up. Sometimes you will be left with inserts that are slightly proud. I usually knock these down with a file as best I can without damaging the deck.
Bonus Step
The cutting edge of the inserts usually pushes the cut away material into the middle of the insert. Not great when it’s mixed with epoxy. I use a bolt to push this resin mixed debris down to the very bottom of the hole.
I keep my finger on the top surface of the deck while gently driving the screw down until I can feel that its squashed against the bottom of the hole without deforming the top surface.
That’s it!
Remember, if you fuck it up, you can always just bolt through! 
