Instead of spraying, get a gallon or so of poly, laquer, or other sealant and roll it on with a roller. The targets will turn a slightly darker brown and curl a little when you do only one side. Rolling the back as well will take the curl out. Pasters and masking take seem to stick on, but the masking tape can take a hard rain better in my experience. I use bags if that is all that is availablr, but it does slow down scoring and taping. Personally, I prefer to shoot non bagged targets, but it is a problem looking for any solution.
Paul : -)#