BranoI hate VogonsPremium,MVMReviews:
OK, so on side A you have two public IPs and LAN 192.168.1.0/24.
On your side be ensure that LAN is different i.e. 192.168.2.0/24.
Then create IPSec Site-to-Site tunnel between site A and site B router.
Add appropriate firewall and policy rules and you should be done.
No need for any port forwarding.
Complete manual with example is here: »ftp://ftp2.zyxel.com/ZyWALL_USG_50/use···_Ed1.pdf
Some additional info here: »ftp://ftp2.zyxel.com/ZyWALL_USG_50/sup···3.00.pdf