Are the tubes constantly being inflated deflated? If not see you need to clean the tubes properly where the letters go. If your tubes are hypalon then use a solvent such as MEK or toluene or acetone etc.
Acetone is fine, don't bother with the others.
Use the very thin conformable vinyl for the numbers warm them up with a heat gun after fixing and smooth down carefully with a cloth.
__________________
But I may be talking Rubbish.
Expurt is a drip under pressure, and the difference between an Amateur and a proffesional is getting paid.
