put tube amp on to shelf of a rack

Go to the gym more.

asvjerrry is correct.

TWO 12VDC 100mm [or 120mm or 140mm] fans  run on 3.5VDC. One either side of the amp PULLING air AWAY from the amps will keep them and the equipment above sufficiently cool.

FAN: https://www.amazon.com/gp/product/B019SY0TAO
PSU:  https://www.amazon.com/gp/product/B01G7KT0V6

IMO, the curved fan blades as shown are mandatory. I've been actively cooling HiFi and other electronics since the 1970's. Curved blades are the quietest in this application.

I have 5 such fans for my 3 tube and 1 ss amps in my Tri-Amped rack system. My media room is sub-40dB. At 1 foot from the amps, the fan noise is neither audible nor measurable. See http://ielogical.com/assets/Audio/FanCtrl.jpg for a "Power Distribution" example.

105 pounds atop a stand not much larger than the amp footprint is a severe earthquake hazard.

Get  SYMPOSIUM ULTRA amp stand for best looks,sound and build quality.

Or, get the Symposium Foundation Rack.  It can support the weight of your amp and there is ample room on the bottom shelf for allowing the amp to breathe and remain cool.  There is plenty of space above the amp that allows heat to dissipate and minimize heating components above.  The next shelf/level above the amp provides plenty of insulation for upward heat from below it, anyway.  You can order the rack to have the upgraded Ultra Platform for the bottom shelf/level which will further provide superior vibration control and best performance from your amp. 
This is a good example for what you could use regarding heat control and sound quality.  However, per your initial question, it still remains that you need to get your amp onto the bottom shelf.  There are other good suggestions cited above on how to do that.