It will be impossible to move such big bed, The gantry is the way. I am sure you will manage to weld it. I learned to weld on my first machine and stick welded it. Did not have a Mig at that time. It even turned good. Think what i am telling you about the Chinese square rails, they will save you some money. In fact last time i bough they were Hiwin quality like, almost :-). But were proper steel.