Question for you fellas.  Do you think 3/8 rebar cut into 4" pieces and spaced 3" would work to secure the air hose to the form using 60# of pressure?

Should work fine.
Rather my forms have a top tho.

  I contacted a Buddy on FB who goes Topless...   

  He said your plan sounds pretty good but to go a little closer with rods around the riser...  He uses 1/2" cold rolled steel cut 6" long (Does not like rebar) and goes about 2 1/2 to 2 3/4" spacing between rods... I think he uses strapping also not rope...

   My personal opinion...  For a 1 1/2" wide form using rope...  I would go 1/2" rebar, 5" long, 2 1/2" spacing and 2" spacing near riser...