My son in law is a crane operator and he was kind enough te lend me a hand in erecting the masts for the antennas. First, we set up the big mast (a long piece of scaffolding pipe attached to two mounts that are bolted into the wall.
My son in law came up with the idea of a jig that helped us getting the mast upright. In the picture you can see it at the foot of the mast. Basically it is a pivoting T-piece where the foot of the antenna fits into. Clever idea!
Furthermore I needed a small mast to have a second point for the wire antenna (3 band MK III). Now the crane operator part came in really handy.
Finally, the antennas are mounted!