Hi,
I tried it once with a 3 by Televue barlow and a 2 by Celestron barlow. This gave me a theoretical focal length of F60 or nearly 18 metres on my CPC 11 F10 SCT as the magnifications multiply.
This wasn't a great success as at that magnification there is never good enough seeing to realise the full potential of F60. So you would get the same results just by using one barlow and digitally zooming, a bigger image but no more detail.
Also since the two barlows were joined together the imaging train was rather long and with the camera connected was probably no longer exactly square to the optical axis, as there was some flex.
I may be wrong but I think you can increase the magnification just by adding an extension to the bottom of the barlow, though I am not sure what the magnification formula is. This may be a 'lighter' way to go.
So yes it is possible but depending on your equipment the results may not be great.
Still you can give it a go and see what happens
Cheers
Paul