Finishing off by Filling wood Grain

On one of your prior posts you mentioned that you crash with regular frequency. This to me is very counter productive to apply a finish that will be short lived. It would make more sense to determine why this is happening prior to achieving a nice looking finish. Using dope and silkspan is still the strongest, lightest solution you can use to obtain a good base finish. If that's out of the question, there are some other alternatives using spray can finishes. I don't prefer them but I've seen them and they look nice but they can be easily overdone and weighty if not properly done. One method that the late Allen Brickhaus wrote in Flying Models was the use of Minwax Polycrilic water based urethane. He would apply 2-3 coats of this sanded in between using a sponge brush followed with Rustoleum gray primer. He actually would lay lightweight glass cloth onto the wood after the first coat but I wouldn't recommend this for a 1/2A. The lightweight glass was attached with the Poly and then when sprayed, Allen used the glass as a gauge as he would sand the primer almost completely off just exposing the glass underneath.

              ONE ISSUE WITH water based products. they can and will warp sheet balsa. Therefore, when applied on a sheet wing for instance, you must immediately coat the opposing side.

             Assuming you have at least 3 coats of water based urethane on the wood, you could spray the primer, offer 20 min dry time and sand the primer almost completely off using 320 Tri-mite paper and a slightly soapy water solution. This would offer the smoothest base for the Rustoleum enamel. Once completely cleaned, light misting coat of Rustoleum Stops Rust enamel. I prefer to set the spray can in fairly hot water in a pot for at least 10 min prior to use. Shake can extremely well and insure all water droplets are gone from the can prior to spraying the model. Apply a light coat onto the model and I mean a light misting coat, no need to even offer enough to cover completely, just a base of mist around all perimeters.  Give 10 min to tack and offer another light coat until model is completely coated. Remember when spraying, don't concentrate on the main areas such as top and bottom of wings and fuse sides. Spray the edges first as this will blow overspray onto your main areas. Then go back over the mains and let it cover in a continuous spray pattern.