I have flat towed almost all my Morgans (Series 1, 4/4, and Plus 8) but not behind a motorhome, only behind my SUV (Ford Explorer). And, I have never towed a Roadster. (Not sure what to make of the air con condenser?)
I attach to the Morgan's lower cross member. Dont know if there is access problem with a Roadster.
Towing is easy but the tow bar (A frame) must be low enough, coming off the tow vehicle, to allow some vertical movement as the tow vehicle goes up and down over bumps. A Morgan without a front bumper is much better than one with a front bumper.
Cheers,