Hi,

I would be afraid that using an elastomer compound would not be any better than the rubber tube or even worse. I’m saying if the rims are not suitable for tubeless tires you may be correctly concerned.
Besides I have never seen that any Flex Seal product seals out anything but water and shown without anything more than static pressures applied.

The rims are probably made of rolled steel into a band and welded across the butt ends along one area.
The center portion like the spokes would be welded to the inside of the rim so I doubt the welds penetration goes through from the inside to the out side where the tire is.
I agree that Spot welding is resistance welding.
Some with or with out fillers but in those cases it is considered skip welding too?

Some steels used in manufacturing rims do not take kindly to just any welding processes either.
You will need to know what steels are there before welding. Acid testing can help with identification.
You don’t want to end up with a stress crack.
Especially within the center bolt circle.
Cracks can develop from one bolt hole and going to the next bolt hole.
A lot of stress flow travels through the center structure during Acceleration, Braking and Turning.

The older bias tires of the fifties and sixties used tubes but tubeless tires were on the shelves by the seventies in upper grade brands.
You had to go a ways to stay with tube type tires eventually.

If you use anything an epoxy or urethane coating is probably advised to be best for longevity.
Both have greater adhesion properties than plain enamels.
Rim rust is probably the number one thing affects a tires bead sealing capability.
A Garden tractor, cart or wheelbarrows tires always seem develop a slow leak but then it’s also goes back to the rubber casing material.
The idea of a Flex Seal product just doesn’t blow a skirt up to get me interested.

Recapping of tires was more popular back then too but installing tubes was like a standard procedure using them.
In those days you could use hot patches or heat vulcanizing on tubes. Later on put adhesive boots were used inside of tubeless tire after a puncture.
Then even plugs came out for the new radials that allowed repairs for flats to be done without removal of the tire.

Somewhere along in all this the tires started using safety bead rims and tubeless tires, won hands or thumbs down, against tubes.
So these tires you found on those rims must be relics!

How old do you think the tires are? Any tubes are hard to procure today even for wire spoked motorcycles.
Maybe there is a solution for those rims that you can get for yours?

DOT requires decent labeling any more.
I can remember that manufacturing dates were not used unlike today.
Even If there were dates they were letters that seemed like a secret code.
Hopefully you have numerals. Consumer tricksters caused the DOT to go to numbers.
If you don’t have them, throw away the tires.

Phil