Fiat Ducato 8: Cable dashboard / engine compartment

Hello, I would like to install a fender antenna in our camper (see appendix). How do I get the antenna cable from the engine compartment into the dashboard? Where/which parts do I have to expand? Are there experience values / existing possibilities? If the proposal of a roof antenna comes: I know that actually only a roof antenna really works perfectly, but for various reasons I don’t want to. Among other things, I would like the 10-year waterproofing guarantee of the Plus I don’t want to get over 3m under any circumstances (the car is 2.95m high). In short, roof antenna does not work. My neighbor has a camper from Knaus, and this has a fender antenna (which is attached to it) as standard. And he is satisfied with the reception. Thank you very much, Markus.