Technically there is a back way into Arches right from Willow springs Rd. It's actually how you got into the park years ago. It is dirt/sand though so really depends on your bikes. Fat tire bikes would be better. We rode our street legal motorcycles in that way.

The Moab Canyon Pathway starts about 2 miles down the highway and runs past the Arches entrance, and all the way into Moab. But you'd have to do the first 2 miles on the shoulder of the highway. And it's a little ways from the entrance of Arches to actually get up into the park.

Once you get back to 191 you can ride the road. But the trails off of 191 can be rather sandy.

There's signs on the trails that say "no e-bikes or pedal assist bikes". Was very disappointed as I ride an ebike simply because without I'd be pushing my bike the whole time.

I don’t think you could travel to Arches from the campsites while avoiding roads, but I’m not entirely sure. The only road around really is the highway that the park is on along woth Canyonland and Moab. You might be able to find a route along the road but on it though since the ground is pretty flat and the terrain isn’t extreme!

It would be an easy bike into Moab as it is 7 miles (if memory is correct) and all down hill. They have a great bike path most of the way now too. The return trip will be a bit rougher, but the e-bike will help there. Arches is pretty close, although a steep incline at the entrance as well. Willow Springs road itself leads all the way into the center of the park, if you are up for the bumpy ride.