How to configure simple network with BOX/Router RV042/Computers

How to configure simple network with BOX/Router RV042/Computers

I don't manage to configure my router correctly, I have some troubles with
port forwarding and I suspect this is due to the router mode I use
(gateway Vs router mode).
Internet Box (Manage LAN network 1) :
- WAN : 128.xxx.xxx.xxx
- LAN BOX IP : 192.168.1.254
- MASK : 255.255.255.0
- DHCP : ON
- LAN PORT : local router
Local router - CISCO RV042 (Manage LAN network 2) :
- WAN IP : 192.168.1.5 (from Box DHCP)
- LAN IP : 192.168.0.1
- MASK : 255.255.255.0
- DHCP : ON
- WAN PORT : Internet Box
- LAN PORT 1 : Computer
- Gateway : 192.168.1.254
Computer
- LAN IP : 192.168.0.2 (from router)
- Gateway : 192.168.0.1
In Gateway mode
All is ok except the port forwarding.
Internet box : port 80 is forwarded to the router WAN IP port 80
Router : port 80 is forwarded to a LAN computer port 80
FROM LAN, if I go to the router WAN IP in a browser I see that the port
forwarding is ok. But when the redirection come from the Internet Box, I
have the feeling that the port forwarding doesn't work and is blocked at
the router.
I suspect this is due to the router "gateway mode". I read that in my
configuration I should use the "router mode" instead because the Internet
Box "should be" the only gateway.
In Router mode
I don't even have Internet access on computers... I don't know what must
be changed, I tryied to change the computer's gateway to 192.168.1.254
(box), to set all computer on the net 192.168.1.0... nothing works.
Is the problem of port forwarding could be linked to the gateway/router
mode ?
How to set up configuration in router mode ?
Thank for help.
If you prefer I go to the cisco community just tell me I will delete this
post.