i used the sup assembly loader to build a rover in the SPH and then attach a Lifter i did in the Rocket assembly building, i don't know how i would do that today, maybe someone knows a trick. Building a Rover in the Rocket assembly building is a nightmare. To land the rover i used a normal lander and docked the rover underneath it. Drop the rover, lift of again and land besides it. I managed do land 80 Ton rovers like this.