I use a lot of needlepoint canvas too! The one thing, though, its not as easy for crabs to climb as i like. Consider siliconing stones on the surface or tying plastic thread to create a better surface for gripping claws.
Replacing dowels is a good idea. Someone else made a bridge out of imitation jenga blocks

Suction cups can be awesome, especially those power locking types. I only advise to use more to lighten the load of each hook, this making your structure more stable. I'd also clean the surface with a drop ov vinegar for a TIGHT initial stick

Crabbers unite!!!