As you would have already thought of building a work ramp outside or a pit inside to service the motorhome and still want the hoist . The barn needs to go up . No matter how you do it , you will need extensive temporary cross bracing to hold it together while it is being lifted . Weather you lift it with a large crane and spreader bar , or jack it up is up to you . You are going to need to fill the space at the bottom , if it were me , i would use Besser blocks to make a wall around the inside perimiter the height you want to go up . Put the blocks on the slab against the inside of the cladding , leaving a space around the Portal legs (the exact size of two blocks wide). You would then need to undo or cut the legs off . I would then lift the barn with the crane and spreader bar and sit the legs on some heavy Galvanised angle iron/Lintels put across the gaps in the Besser blocks and let it come back down . You would then need to fill these gaps with blocks . Bolt the legs through the angle iron , and put threaded rod through the angle iron , through the blocks and into the DynaBolt hooks you have already put into the slab to secure the barn to the slab then fill the blocks with concrete . As you can't have a crane hired all day , this is the only way i can think of to do it .
On Edit , Just looking at BigE's post , you may call Besser blocks , cinder blocks .
