Why use a rust encapsilator when ya have no rust? crusty under-carriage that you're not gonna blast, sure.. bare steel, nope...
Drives me nuts to see someone go thru the trouble to do it right by blasting it, then not use the proper priming procedures...
zinc chromate, epoxy primer and urethane topcoat is the proper way to coat bare steel..... Tho it is a more expensive solution, but if you've gone thru the trouble/expense to blast it, a few more bucks on materials seems to be paltry imho.... throw in some metal conditioner to be exceptionally anal...
I've been using POR15 for 20 yrs, great product, but it has it's purposes and limitations... Even when using Metal-Ready and a good topcoat, there are better choices for raw steel...
Don't get me wrong, the fact you blasted it should give you many trouble-free years, as long as you topcoat it.. But as far as a bare steel, coating system I prefer more traditional methods..