I am not an expert in outdoor installation so I can’t really say. But if you think your gw antenna is the highest point in your area, it might be a good idea to have one.
just for information I also had some MIC mismatch on TTN, solved by generated new keys on both side. pleas note that TTN fair use allows only 10 downlinks/day so confirmed packet on TTN every 5 minutes will work less than one hour so in case of confirmed and testing chirpstack is the way to go 
Hi @Charles ,
Thank you for sharing the info. I have started using Chirpstack now. It works very well!
Another solution is also to use the RAK7258 cheap GW and the network server included into. For testing it’s simple, easy and cheap, no need chirpstack installation nor cloud connectivity.
Thanks for the idea.