i have made 2 pans (63 and one of my convertible )
after sand blasting
i prefer to cover them with por15 silver.
uv resistance is not an issue for floor pans as never face the sun directly..
one option is to sprey a coat of ordinary uv resistance colour on top of POR before dry.
after sand blasting nether por15 needs to make the 3step proceeder.
You can just paint directly with por15 on sand blasted area (i had this information directly from por15 company )
for the bottom of floor pans after por15 i apply and 2coats of ''hard nose '' paint.
it is a very strong paint that dont peal of from rocks...
(it is a por product)
recently i find and an other product that is very good as a primer ...
it is called ''red-brown'' from STANDOX company .
it is a very good german product so maybe this is more usefull to european members of stf