I've posted this before but on my first camper (fwc ranger) I used lolo bar hooks mounted to unistrut which was then mounted to plus/riv nuts into the camper frame. Felt solid enough for reg bikes but I would personally draw the line short of carrying any heavier ebikes. I ran a cam strap to the roof rack for a while when testing it out... I would just use my front hitch if I wanted to carry heavier bikes if the back hitch isnt available. We use a swingout rockymount rack now that we have a camper thats short enough to access the hitch (fwc hawk).
If you dont want to use a front hitch rack, I did see these recently: https://squareonecreations.com/collections/sideride-bike-mounts . You might be able to fab something up if you can figuure out clearance of the bars. It might still be a bear to lift a heavy ebike up but maybe easier than a vertical oriented fork axle mount and it would certainly be sturdy.
If you dont want to use a front hitch rack, I did see these recently: https://squareonecreations.com/collections/sideride-bike-mounts . You might be able to fab something up if you can figuure out clearance of the bars. It might still be a bear to lift a heavy ebike up but maybe easier than a vertical oriented fork axle mount and it would certainly be sturdy.