Bed to frame insulator locations?

[RQ Jay]

Having removed my fleetside bed to complete my c-notch, I had just a single bed insulator disc left on the vehicle...the others either were removed from the previous owners or cracked and lost...

I found some replacements at 5 dollars each, and it looks like I will need 4 for the job.
Could anyone tell me what 4 areas these go to? I plan on just unbolting the bed and jacking the sides up to place them there and have to do it somewhat blindly..

Also, is there a better alternative than these 4 discs? Like using a 1/8" thick rubber strip?

Thanks