Disc grinder, rotozip, dremel. Easiest and quickest. But be careful and use all the protective equipment, goggles, mask, gloves etc.
But also depends on what type, if blakes, cut the bolts with a disc grinder and pull them out, need new bolts anyway. Or split the nuts with a nut splitter ofr chisel and knock the bolts out.
When all else has failed I have used an angle grinder to grind away the flange on the outside of the hull. Only takes a few minutes but obviously you need to be very careful not to damage the hull.
if its turning as you try to undo the nut and
if the fitting is brass and has tabs on the inside i found a bit of tube that fitted snuggly up it cut 2 slots ,then was able to hold it with pipe grips or make it into a rt angle like a wheel nut remover, and undo the nut on the inside
if thats not possible you can get a handle that holds a hacksaw blade on its own or squash/crimp a bit if copper tube around the blade and cut through,
if they are plastic the coarser the blade the better .
if the nuts are hard to get at or too big for normal tools its probabally safer to cut through as much of the nut as you can with a hacksaw before using a chisel,if you can boil a kettle pour hotwater on the fitting first as the heat sometimes helps to free the nut off a bit
hi steven ,there were getting to be too many skeletons,didn't realize you were using it as well,if anyone is using a dragon that is the same/similar to the one i have changed too apologies let me know and i will have a rethink