I learned this trick a few years back, and now that I have some machines I'm working on ... was able to photograph it. The Cardboard trick as demonstrated on another post works great too, but this is easy as well and only requires one person, a roll of painters tape and your machine to be restored.
1)Lay the machine on it's back, cut and lay in insulation, sides first. Before putting the back side insulation in, take a roll of blue 3m Painters tape (works best for me and won't damage paint). Stick one end to back of machine, as close to the side as you can, pull the tape up and compress the insulation to the side and pull tape around the side and fasten to outside of machine. Do this all around sides, spaced out around 4 inches or so apart... Lay in your back side insulation, which will hold the back of insulation in place.
2)grab the liner and slowly work it into the machine.. let the air escape through the holes in the cabinet that are already drilled for the condensor... do this slowley and don't force it, just work it in by applying pressure....
3) it should slide right in and insulation should remain in place as long as your tape on outside of machine holds...
4)once the liner is nearly seated properly... simply grab the outside peice of tape from edge, lift off and pull straight up and out and it will peel right off and leave insulation in place.
5) finish installing liner with spacers and such and walla, your done... see photos.. hope this helps.

That is a great little trick , I will be using that on my next projected
 Plus I think this would work alot easier on the upright machines.
 Just a question did you lay something under the machine ??

 Sorry it looked like paper .

That's a great idea as well as the cardboard!

I am not certain about all machines, but I've used R19 unfaced for my machines, the width works well for the cabinet size and it fills nicely..
Before you dig into that SLider... read someo other posts on SMC here and make sure you know what your getting into... That is one of the hardest machines to restore, due to the cooling system coils inside the walls of the machine.
Good luck, Thanks for checking in, and welcome to SMC!