It is not hard. I use T-NUTS. In plastic I get my location figured out getting as close to the center of gravity as I can, usually this is near the front action screw. I get the holes drilled then pack the inside with JB weld, I then push a piece of all thread rod from the outside through it, clean the threads,screw on the T-NUT and pull the t-nut down until it if flush with the stock. I do the clean up inside and out, grease up a screw and make sure the threads are good and clean. After it is set up your good to go. Now if you decide to remove it all you'll see is a threaded holes from the outside. 1/4x20 is what I use.
If wood just drill the holes and countersink the inside getting the depth right. most hardware stores will have them in the bolt aisle.
Good luck