Embarrassing....

[Sailor Steve]

A Tiger tank weighed about 75 tons. Even a Maus weighed only 190 tons. A heavy lift flatcar can carry about 100 tons. When the 30th Flotilla was created on the Black Sea, six Type IIb boats were shipped by canal and road, using special transporters. Even stripped down, the hulls weighed 140 tons each. The operation took five months.
https://en.wikipedia.org/wiki/30th_U-boat_Flotilla

A Type VII u-boat weighed roughly 750 tons. The super rail guns Gustav and Dora weighed 1300 tons, but special rail lines had to be constructed just to move them.

I am sure they could even disassemble it and reassemble it at it's destination.

How? Cut them up and re-weld them at the other end? How structurally sound would they be? If it could be done, how many months would it take? It would probably be faster to construct a u-boat assembly yard in Italy. The only reasonable way to get the boats there was to sail them and hope for the best.