The last place you want to go is a welding shop. Don't weld a baseplate to the frame. Baseplates come with good instructions that any automotive mechanic can easily drill necessary holes and mount the baseplate. I'm just an old John Deere mechanic and I've installed three myself. All were done in my driveway in just a couple hours each.
Call chief's RV in Tri cities. I doubt whether there is any one closer that knows what they are doing. 800 345 1819 Roadmaster relocated to Vancouver, WA.