You can do a very quick look at the tube currents and I have done it before, get onto a bright star eg Rigel, defocus so your star takes up 3/4 of your screen and then with a DSLR put it on live view and then youll see the waffling air coming up the side of the tube. for added affect put your hand in front
. You should also be able to see if there is the boundary layer that you talk of clive coming off your spider vanes as they too will show the refractive index changing you will see it almost like clear smoke coming off!
I sometimes utilize this method to see issues. I think too that drawing the scopes volume of air though on a regular basis sucking in the cool air above the ground and exhusting though the rear would be extremely benificial as it would decrease the depth of the boundary layer as the tube/vanes and the like will not influence the air so far out. If sufficiently strong enough the air would not let a boundary layer really form over the face of the mirror or it may sufficiently stir the air on the mirror surface and hence decreasing that nasty thick layer of warmer air.
It would also aid in thermal equilibrium of the mirror.