Sonnie:

Yes, yes, yes. You shouldn't have any problems with having a second mount.

a. Just make and attach a set of "dob" side bearings, when you want head out for a quick look, unbolt your tube, and drop it into a dob rocker box or...

b. If you don't want to modify your tube by bolting something to the side - make a open ended "box" that your tube drops into (make the top removable with screws) put the side bearings on this box and drop it into the rocker box. Make it a close fit and you can balance the tube for dob use.

Go for it!

- Tom