it seems a little complicated.
can you draw a simple topology and see if someone could figure out the problem

I have warehouse A and Warehouse B both connected independently over IPSEC VPN to the main office. People at the main office can print and connect to pcs at either warehouse. People at each warehouse can login via remote desktop to machines at the office or print to the office printers. How do I allow traffic to flow from warehouse A - through the office - and to warehouse B? Sometimes the warehouse manager at A will need to print a document at the loading dock of warehouse B. Right now I cannot see any devices past the office. I did have a 3rd VPN set up between warehouse A and Warehouse B but the internet connection at Warehouse B is too slow to support 2 VPN at the same time. It would pick 1 and drop the other in a random fashion.

Router at Warehouse A is a Cisco RV180
Router at Warehouse B is a Cisco RVS4000

These are the first VPN I have ever set up so please be as thorough in any explanation as possible.

Is there a reason not to simply create an additional link directly between warehouses A and B? I think this is the only way to do what you want?

Every time I have tried that the warehouse B link drops one or the other connections. I think it has to do with the available bandwidth. That building has wiring form the 50's and we barely get 1Mb download speeds from our ISP. upload is around .35Mb. I thought if I could create a pass through from one vpn to the other at the main office it would diminish the effect of low bandwidth.

I'm afraid I don't see how to go via your "Main" router, you could link via a static route if "Main" was a PC, but the router won't support this I think. I don't see why the bandwidth should cause problems, it's only one additional VPN client after all - might be something flakey in the Cisco firmwares? Are they both up to date? Can only advize to keep playing with the VPN setup (keep alives, DPD etc.). Good luck :-)

Setting up what we have dubbed "The Triangle of Trust" works fine for a few days usually. Then the link between either A-B or Main-B disconnects. Not the same one each time or after the same amount of time. We have run for over 2 months with the 2-way configuration without having to reset either of the connections. I have a feeling it has to do with a combination of factors not the least of which being the model of router at location B.

Thanks for chiming in.