Dennis, you have to keep the air circulating. A small, (10"), fan will do. Just leave it running on low speed, or you could build a speed control unit for it. A light dimmer will suffice here. Just mount it in a 'Jiffy box' from D. Smith's with a 240 volt socket as well.
ving, if you really want a lot of silica gel, goto any shoe store, eg; K-mart prob. best & ask them. You'll end up with literally 'a shoe box full'.
L.
ps. & IMHO, there's nothing wrong with a plastic cover to keep the dust out. Cloth just doesn't do it. (lets dust thru!). Just air/dry your t'scope before placing the plastic cover on.
pps. I 'hook' a 1/4 lb bag of silica gel inside the tube every time I pack up.