Fuel proofing hard to reach ARF
You can also put a good amount of the sealer you're using in there and then roll the plane around at various angles to move the puddle around. A dentists mirror is really handy for seeing where the wood is still dry. You can get them at harware stores.
Polyurethane is already at a good viscosity for this and is fuel proof.
After everywhere is wet, you can use paper towels in to sop up the extra.