Trying to keep it inbounds is unlikely to have satisfactory results. I'd suggest selling it at a garage sale or something while it still looks nice and getting a dwarf poinciana (Caesalpinia pulcherrima) for container culture instead.

Here is a link that might be useful: http://edis.ifas.ufl.edu/st107

Good Advice!! My RP is probably 40ft all and nearly as wide. :o)

Hi
I grew a white form of RP in a pot for over 10 years . While kept it in bounds it did not flower.. Has since been planted in a neighbors yard and I fear that it is permanantly
flowerless though it's tripled its size.
Dwarf will flower regularly at less that two feet and you can prune it any way you choose !! much better choice and there are several colors. gary