Please note that the Tailscale binaries for OpenWRT are pretty large (even if you cross-compile them with compact and strip). Your router might not have enough storage for it.

If that's the case, you might work around it by only storing the tailscaled binary on persistent storage, because that's the daemon which runs the actual connectivity. The tailscale binary is only used for making configuration changes, you can copy that to RAM disk, use it to set config params, then delete it.