Are concurrent Client Mode connections possible?

I have a TP-Link TL-WR2543ND v1 router running OpenWrt 18.06 that is using wifi client mode to connect to a Blackvue dashcam in the car. The dashcam is acting as an AP and there is a Windows Service running on a computer on the network that downloads the video files from the dashcam each time the router makes a connection to the dashcam. This has been running well for nearly 12 months now.

I'm about to get a second car which will have a second dashcam which will act as a totally new access point. I am happy to buy a second router to configure for the second dashcam if needed. But i have also been trying to work out if my router (or any router for that matter) could be configured with two concurrent wifi networks operating in client mode to connect to two different access points (i.e two dashcams)? If so, how can this be achieved?

I'm reluctant to start playing about with the configuration without having a decent idea of what im doing because the last time i messed around with the router, i spent another 2 days trying to get it working again.

Very unlikely, most wlan chipsets can only set up a single STA (client) interface at a time (for a couple of technical reasons, among others because the AP decides about the channel and not the client, while a single radio can only use one channel at a time - another because this isn't a common scenario for vendors to care about), iw list will tell your about the details for your chipset. I'd excpect this interface combination for your device:

        valid interface combinations:
                 * #{ managed } <= 2048, #{ AP, mesh point } <= 8, #{ P2P-client, P2P-GO } <= 1, #{ IBSS } <= 1,
                   total <= 2048, #channels <= 1, STA/AP BI must match, radar detect widths: { 20 MHz (no HT), 20 MHz, 40 MHz }

With concurrent dual-band APs (those that have two independent radios, instead of the single dual-band radio in your tl-wr2543) you might be able to use the 2.4 GHz wlan card for one dashcam and the 5 GHz wlan for the second (but that would require your dashcam to support 5 GHz).

Personally I'd probably try to employ some kind of tricky time-share solution with your existing device (scan for APs regularly, if $dashcam in range connect, transfer the data (from the router (e.g. USB storage), because that way you get feedback when the transfers are complete), disconnect, go back into active polling mode - add some more logic to avoid repeated transfers), but that would require a little experience with linux and some shell scripting to get working.

Thanks for the reply. I did think it might be a long shot. I've dug out a spare RPi3 and will see if i can get that to work as a second client mode device which will save having to go down the tricky time-share route.

As long as your router should only manage multiple uplink accounts, look for travelmate Travelmate support thread