I started using PolyU to fuelproof firewalls, tank areas, etc four years ago. Used MinWax. It seemed to hold up OK but if really soaked (like, fuel tank leaks) it would eventually soften some with 10% nitro. Never actually got to the wood. I tried to use the MinWax to apply fiberglass and, while it worked, I found (as have others) that it tends to be "soft". Holds paint well but tends to "dent" easier than Epoxy.

Two years ago I switched to Flecto's Diamond wood finish for floors. It is a water based poly-u and is harder than an old miners boot! This stuff works great. I have not had it soften using 15% nitro and I even soaked some covered wood in the fuel. It also glasses nicely and, in my opinion, is as hard as epoxy and takes paint easily. I painted a test piece of balsa white, brushed on one coat of Diamond poly-u and waited to see if it would yellow. It has not and I left it out for two weeks in the Oklahoma summer.

The downside is that it is currently selling for around $38-42 a gallon (Lowe's, etc). I know it is available in quarts but I have not seen them at my local Lowe's. I got a gallon from a person "in the trade" for $28.00 - two years ago.

Just my .02 from my experience.

As the lawyers are prone to say "... your results may vary ..."

Dan