[AcampoDave]

I mostly used epoxy primer on the longbed and tried to prep like I would for any automotive paintjob blocking it out thru the use of a contrasting guide coat. That truck was thinned with mineral spirits as the weather was very hot.
The almond shortbed was done with Rustoleum branded primer following the same proceedure but I thinned it with acetone instead which Ive come to prefer due to it's faster dry time. I have no ratios to give you as I just kind of "go for it" using a few test sprays and adjusting the ratio as I go. I would say 30% thinned is a good starting point though.

I had to shoot the longbed twice as my first go at it was disappointing. I didn't block the primer well enough and the orange peel look showed right up in the paint. No biggie though, I just blocked the paint down by wetsanding to a smooth finish and re-sprayed it. It was my first try at painting a vehicle so I didn't beat myself up over it or anything. Even then, after the second coat, I had to color sand it with 1500 grit and buff it out.
The almond shortbed went much smoother because I had learned from my mistakes. It was a one shot deal except for the roof which became a mess when a rogue gust of wind blew a bunch of birch tree seeds into my fresh paint. I sprayed the white first anyway so I just blocked it down and reshot it prior to the color. One thing I learned is; on a two tone job, its beter to see the white color thru to completion before prepping the base color as overspray will just coat your prep work anyway. Edit: recoats must be done within 1 hour or after 48 hours or the base coat will "check up" underneath when the topcoat softens it up