I need a quick fix for a paint job. It will be redone later, but does anyone know if polyurethane is fuel proof?

I use Nelson Hobby Specialties System Three water based Polyurethane on several planes. It is naturally fuel resistant and with a supplied cross linker it is proof up to (by my test) and maybe over 15% nitro.
Others have stated that poly-u paint from Home Depot, etc. is, but you'd best test a sample and see for yourself. It really depends on the paint.