Jferreir
Jgiacalo makes good sense. he tries a lot of DIY this & that's... I'd listen to him if at this point in time you are seeking inexpensive isolation gizmos... or any for that matter.
The Holy Grail in this past time is always going to be... "Try it and see!"
Personally, I'd say pass on the felt for vibration control.... works fine inside speakers, and here or there for airborne or acoustical treatment help, but it doesn't hanndle weight.
Want cheap? Stoppers. Simple drain plug stoppers. Cut off the eye the chain goes thru and use 'em. Available in lots of different sizes and cost a buck or less, each.
Footers are placed under gear for two reasons... convection cooling and damping.
Get a tube of Blue Tact and make your own 'balls' to put under the gear footers. It's widely recomended for use with speakers on stands.
The idea here is to try something. you'll be better off buying an MDF rack from Big Lots over using the one you speak of here. or two of them side by each. About $20 $40 each.... until you can get a properly damped rack.
There are literally tons of threads here and reviews too on iso devices. I even posted one myself. Do a little searching of the archives and you'll see what other's use or have used. It will or may suprise you what sorts of goofy looking items can actually do to help damp or isolate your gear and/or racks.
But if you don't try any for yourself, you'll just never know. Heavy, solid and as nonresonant as possible are what I seek in a rack. give 'em the knuckle rap test and see if it rings or rattles... it should be quite dead.
Good luck.