First...there is a new version of the Rustoleum bedliner out. I think it's called "Delux" or something like that. You will know it by it's price tag...it's almost double the cost of the regular Rustoleum bedliner. It's much thicker than the original.
Stand back at least 12-14" when spraying, and don't hold the can still. Keep it moving and don't go slow. Start spraying the air in front of the end of the stock and move the spray across the stock in a steady movement. Don't stop or slow down until you are spraying the air on the other side of the stock.
Several light coats are better than one heavy coat. This takes patience! However, each coat dries rather quickly. You can re-spray in about twenty to thirty minutes. This doesn't mean the first coats are fully dry, it just won't create "runs" when you re-spray.
When you have achieved the desired look or texture, let the stock dry for at least a couple of days before any heavy handling. Full hardening/curing of the bedliner can take a week or more. The finish can be "soft" for several days after spraying.
Don't leave the masking tape on too long after spraying. If the bedliner dries too hard, it will adhere to the tape and peel off the stock when the tape is removed. Thus, the practice with the above mentioned 2X4 board. Further, an Exacto knife, or razor blade, can be run along the masking tape edges to ensure no stock peeling takes place when the tape is removed.
Patience and attention to masking detail is required. This isn't an afternoon job, start to finish! Take your time, it pays big dividends.