Travelmate is the solution I think you want... what wasn't working when you tried it? I don't use it frequently, but it has worked for me whenever I've needed it -- you just have to follow the directions for the setup process and it should be good.
If it's not working (or if there is a feature mismatch), consider raising that issue in the support thread for the package:
I think i need to take my config back to base and get that element working first,
I'm liking the configurability of OpenWrt, but i'm also climbing a fairly steep learning curve with it so my config is probably a bit messy at the moment
The main issue i had was that when an SSID "went away" it wouldn't try any of the others and just kept trying the one it was previously connected to, even when the SSID was available, it connected but the interface was still marked as "Down" in MultiWan Manager
I'm going to get to know it a little more before i try again because it's worth the effort for the features it will give me
Travelmate is really setup to handle the situation where a known/previously used SSID is not necessarily in-range... it will progress down the list of preferred SSIDs and it will gracefully fail if it doesn't find one available. This is critical for devices that have a single radio device that is to be used in both STA and AP mode, but it is useful for devices with multiple radios, too. I don't know offhand if it has connectivity detection (i.e. beyond the physical/wifi connection, can it detect if an active internet connection is possible?)... that may be in the documentation or support thread.
the multi-wan manager may be having trouble re-establishing the wifi connectivity once connected. This would likely be an issue of the priority and failover configurations, but I don't use mwan so I'm personally not going to be of much help.