Be advised, that RUT955 is supported by official openwrt. I have done custom firmwares for various large industrial IoT-fleets, being remotely controlled using customized methods (https, mqtt etc.). Even as replacement to Teltonikas stuff, because of RMS reliability.
Custom firmware based on official openwrt has the advantage of being totally open source, which is not the case for Teltonikas stuff.
Another advantages is the community support of openwrt, getting rid of redundant packages and newer, more secure Linux kernels/packages.
Send PM, in case of interest.