As a former user of Ziebart I never recommend spray in with a wash.
What Ziebart would do is to wash the undercarriage and then not allow enough time for the nooks and crannies to dry. They would then encapsulate the water under the spray on material. Which is why my formerly rust free Chevrolet Suburban fell apart 18 months after treatment. The frame and most of the floor rusted through.
If you must wash, give it far longer than reasonable to dry. If there is ANY water trapped under the sealant you will have a hole in 12 - 18 months.
In the bed I might use the spray on but also use the liner. When the spray-on gets a hole in it you can't always see it and if you keep re-spraying it you add useless weight to the machine and eventually end up stripping it off and starting again. If you don't notice the hole then you start developing corrosion and then if you seal over it and then you have a real problem. If you trash/wear out the liner, you can always replace it easily
Stick with the liner, grease the bed underneath it with axle grease (thin coat) and if you really need to soak a small mop head in 90wt and swab the underneath with that. Then park over newspapers for a few days. You could also use spray-on white lithium grease in the hard to reach spots.
If you still need to spray the under carriage (road salt need to come off?) then I would really think twice about washing it and spraying it in the same month - really. I'd just as soon encapsulate the dirt and dust.
I had to throw out a truck with 110k on the clock because of just this kind of thing. If I can stop it from happening to someone else then, good.
Either way, have fun using your machine.