Bit late to the party but have you considered using SteelIt on the chassis?
I was going to do mine in 2 pack but ended up blasting it with a pot blaster (a horrible job and one I won’t do again in a hurry) and the using SteelIt aerosols.
Coverage is great and really happy with the result.
If I was going to do it again would use a gun as it is a lot cheaper - might buy a quart and do the bed rails, rear axle etc - but if you don’t have the facilities 6 cans will more than cover the chassis etc.
Chassis blasted
Pictures are after 3 coats whilst it is still a bit wet.
Looking forward to your progress, going to be a nice truck.
P.
