yellowGT POR15 alone is just fine the frame & engine bay doesn't see the sun much so chassis coat isn't realy that necessary unless you drive around with the hood off. So answering your question
No, but POR-15 has an ultra-violet sensitivity and must be topcoated if continually exposed to sunlight. Once topcoated, POR-15 will remain effective for many years. 
Right off their web site..
POR-15 likes rusted surfaces best. Seasoned metal and sandblasted metal are also good. POR-15 does not adhere well to smooth, shiny surfaces, but will adhere well to those surfaces with the proper preparation.
http://www.por15.com