Rub is easy :P I just place my rub ontop a heatmat that covers half of the bottom. I keep all my probes outside the rub but make sure they are weighed down and are touching the edge of the rub which is the hot side. Cold also follow the flat faun guide and have the heatmat out like in the guide but the probes inside.
RUB is essentially the same really. Poke some breathing holes in, pop the heat mat in 1/3rd, thermometer next to the probe and all :)
And personally, I don't see why it's so hard to just gradually move the snake up the sizes as they go. You can get all the sizes needed really cheaply if you use tubs and rubs with a bit of modding :)