Hi,
set interface ethernet0/0 vip interface-ip 3389 "RDP" 10.0.10.112 <-works >>>>>>>>>> So, it works if using the default 3389 port?
If not, then I would suggest you to try get it working on 3389, before going to a different port.
Few more checks:
1. confirm custom port is not one of the ports FW uses for management (80, 443 etc.,)
2. the VIP policy is on top of the policy list
3. check policy logs to see if there is any activity
4. if you see one directional traffic in policy logs and no response from server, try enabling source NAT with I/F IP on policy
5. no blocking of custom port between client machine and FW