2 wan - ipip - 2 wan

Hi, can anybody help to solve the problem.
I have 2 offices, both of them have rb3011, 2 wan (simple failover, different distance in routes). all wans have have static “white” ips.
I have ipip tunnel from one office to other and all works good, but this tunnel is managed by one ISP (in ipip settings it is impossible to set domain, only ip).
Now i should make failover tunnel between 2 offices using 2 wan in each office.
thanks

So if you have public IPs, what is the challenge in building a second tunnel?

There are som local services that are not very secure that should be available from both offices, that is why i should make a tunnel or smth like this