MDF Rack dampening question

Actually, MDF can work well when used properly, but its use in lesser designs has given it a bad name. What you should be careful of is mixing different design philosophies in regard to vibration control. Basically, you can either attempt to drain vibration as directly as possible or attempt to damp it at each stage. I prefer the first but I have used the other successfully. But a combination of the two is seldom successful. It also depends on the components you are using. Suspended sub chassis tables like dampened platforms much better than rigid tables. I have noticed this with VPI. The new tables have different requirements than the older ones. I would consider Kitty litter if you wanted to fill the tubes , I prefer it to lead or sand, Use of good cones under the shelf system or the individual units will help. You can combine this with use of maple blocks, Timbernation and Michigan Maple Block are good sources. Controlling vibration is a very critical element of good sound and there are several approaches , just keep track of what you expect each element to do.