Love the commitment matey.
I remember making my lowered floor pans and I just undercoated them, then chassis black on the inside and that nasty tarry anti-stone-chip stuff on the underneath and that worked a treat.
One lesson I learnt on a rainy trip back from a show that is worth sharing is, don't forget to drill some drain holes at the lowest points and make sure that the holes are fully painted/grommeted to stop that bit rusting as there you are expecting water!