Having done a bit of research, I have found some gasket material for the forward main hatch and the salon hatch that seems promising (and cheap). On the McMaster Carr website (
www.mcmaster.com) I have found a 6' length of 3/4" tubing for $9.35. This would be used for the tubing that was described as 11/16" (which may have been 3/4" to start). The part # is 4339T14.
For the 1/2" tubing, 4339T12 is the part number. $6.30. It is soft but it is durable. If for some reason it turns out to be too soft one could either squirt it full of silicone or put a thin line through it (if it is compressing too much). Incidentally, don't use silicone to seal the gasket to the frame. Silicone as a sealant is a seal waiting to leak (and not too long from when installed). You might try a butyl rubber sealant for a long lasting and waterproof seal.
Incidentally, if you have never perused the McMaster Carr website (or voluminous catalog) you may be surprised to see that they have most everything for industrial use. Many things may be useful on our boats.
Falco
#198 VANORA
Dunedin, FL