when you say "non barbed" are you talking like a straight piece of ally pipe hose clamped?

If the hose and stub are the correct size, it will not need sealant-if it does there is something wrong with the hose, maybe damaged at the end or more likely just a little to big and pinching a touch under the clamp.

When double clamping, put each clamp opposite way-each screw fitting opposite sides. Then if it pinches, the pinches 2 dont line up.

Also for something as important and inaccessable as this, try and get the SS clamps that have the thread stamped in the band rather than the ones where the thread is a series of slots.

These ones are notorious in the marine industry for breaking without notice under load, both types made by Tridon and others and not much price difference.

I'll chuck a photo if your not sure what I mean?

Also, the clear plastic (vinyl?) lines really shouldnt be used for hydrocarbons as far as I know. Get the proper stuff from somewhere like ACM in Freo maybe?

 is used in the aviation industry. Very pricey. I've done one custom fuel tank and was sent to jandacot and was able to purchase over the counter out of date tubes for around 10 dollars each. Can't remember the company but it was a supplier for aviation parts

Sounds like that sealant is "Stag" used to seal treaded fittings, it could be something else but being red that's what springs to mind.
I was taught never to use any form of sealant on a clamped hose fitting.
The reason for this is that when sealant is used, before it sets it acts as a lubricant between the fitting and hose. When you tighten the hose clamps, instead of the rubber clamping down on the fitting, the (due to the lubricant) rubber or plastic squeezes out around the clamp and not as much clamping force happens.
If you use plastic (I wouldn't) and have to heat the tube to get it on, don't tighten the clamps until the tubing has fully cooled, it will also squeeze out.
Two clamps per fitting sounds a good idea, don't have them lined up, i.e. offset each clamp about 45 - 90 degrees, because a hose clamp doesn't clamp as well under the worm screw.
I would use a good quality rubber fuel hose on all connections.
Also if you are keen, and are attaching stainless or copper tubing, run an earth wire between a point on the tank, under each clamp, to each fuel line etc. back to a common earth so all the fuel components are a common potential.

I'm an ex aircraft engineer, and while it was a while ago, I would have got a goog kick up the arse if I used any form of sealant on the threads or fittings. the reason that it could get into the carby and cause big problems. Maybe things have changed.
There was a sealant used when converting the cavities in the wing into a fuel tank, a two pack rubberizing compound, brushed on over joints and rivets, but nothing on fittings.

I'm up for new fuel lines as well, I also have the clear plastic ones. They have the braided mesh (nylon?) interwoven between the inner and outer layer of the plastic, and if my memory served me correctly a yellow and blue stripe running the length of the hose, not sure if this is some sort of industry identification mark or just for aesthetics.

They have become very hard, although they show no signs of perishing I am concerned about them splitting.

I would be interested to see how you go with regards to finding some suitable hose.

With regards to hose clamps the ones RobH refers to with the slots cut into the band to form a thread, also have a tendancy for the hose material (especially softer compounds) to bulge out of the slots not doing the hose any favours. For sure get the clamps with a solid band and the thread stamped into it.

 Ok so thought i'd update this,

The clear fuel lines ARE NOT supposed to be used anymore, apparently if they are used and you have some sort of mishap, insurance will not cover you.

From what i can gather the new standard is 'A1', and the under deck fuel lines are a black double walled rubber hose with weaving in the middle.

Also the fuel filler hose that was in my tub is not considered suitable anymore either, it was a black hose with red stripe which is apparently fuel/oil delivery hose and not suitable in the event that unleaded actually 'lies' in it, which mine does as the filler is in the side of the tank. oh and this hose has been disconnected since saturday with nothing in it and still STINKS like fuel. This has also been replaced with a marine grade fuel filler hose rated to A1.

Got all my hose for Henderson Hose in Henderson. A bit of a trek for me living nor but worth it for the right gear.

And from what i can gather a sealant is not necessary with the right hose so will just be double clamping.

Steve