I use the Thule ProRide racks on the roof - they are pretty good - not perfect but strong enough for an ebike in my experience. The pain is putting the bikes up there, even with a folding step and a helper
You can get hydraulic lifters, I have seen them used really effective with tandems - but boy are they pricey!
You can get rear racks that bolt behind the tow ball casting and lift the bikes up out of the way of the caravan - not familiar with them but I have seen them. Also seen folks put their ebikes inside the caravan when travelling . . .
IMO strap on style rear racks are only really good enough for local transport - the boot lid Thule 9103 I have does not use straps, it is one of the better ones but I only use it for quick trips.
My folks had a big bike shop in Devon and I used to help out in the holidays. Every summer we had people in the shop buying new racks/bikes after their rack/bike came off on the motorway. Straps move, or unhook, or folks plain put them on wrong