I had a Jayco some years ago and used 4 cross bars from a yackama rack to carry my Jocassee Kayack and two mountain bikes on top.
Seeing your pictures sure brought back the memories.
I used to drag mine everywhere behind my Rodeo. Too bad all my pictures are in my crashed hard drive.
I used four cross bars to spread the load evenly across the roof, as you've probably thought of.
The roof carried the weight well as it was all carried on the edge of the frame.
And of course the frame being wood was a concern. After a few years it did have a problem with it sagging because I put a 1500 BTU AC unit up there. It was only rated for a 1350 btu unit. I liked to camp in the desert. Nothing like being able to camp in Death Valley and be able to relax in a cold camper after a long hard mountain bike ride and a shower.
My Pop Up was a hit with the lady cyclest!:wings:
Always a crowd around it after a hot ride. I ended up adding an exra propane and water tank to have enough water for more showers.
Been thinking of getting another one, only used this time ,and building a stronger frame to mount under the facory frame with bigger wheels and axles.
For the money, a Pop Up Camper is a nice way to go.
If you stripped the wood frame off and copied it in steel tubing you could have more strength, but I would wonder if the weight might be too much. Maybe not if the tubing was thin wall.
Curtis