Thanks in advance for any help.  That said, this is complex and I won't be surprised if there's not much I can do.  Hopefully I can explain it clearly.  Bottom line is that I'm looking for diagnostic tools.  

My environment is fairly unique.  I am experienced with networks although it's not my primary skillset.  Computers are my primary skillset and after a few decades it's inevitable to have reasonable network skills.    

I travel in an RV. I have a server for storage, a couple TV's, a printer and a laptop.  It's far easier to keep a local network running (192.168.1.X) - ASUS RT-N66U running stock code).  The WAN port of the router/switch is connected to a TP-Link CPE210 set up as an "AP Client Router".  Most of the time this works.  I pull into a campground, connect the CPE210 and my local network has access.  There are sometimes challenges with authentication but I can usually log in with my cell phone and then use my Cell phone MAC address on the CPE210 (MAC Spoofing is a great feature).  Occasionally I think I have problems because (I think) I'm double NATing. The CPE210 is 192.168.0.X.  

Often campground WiFi is terrible.  For those occasions I have both Verizon and AT&T hot spots.  Verizon despite many towers seems to have a weak infrastructure with bandwidth challenges.  I can rarely connect the CPE210 to Verizon.  AT&T seems ot have a more robust infrastructure, with reasonable bandwidth.  About half of the time I can connect the CPE210 to AT&T.  I've been unable to define a pattern.  I do think a strong signal helps but that doesn't really make any sense.  

Today - as part of troubleshooting... I usually keep the CPE210 WiFi turned off.  It's connected to the ASUS Router via a cord.  Today I connected to the CPE210 WiFi and the device had no Internet Connectivity despite the AT&T Hotspot having a good connection.  It's working fine with other devices.  That suggests the problem is HotSpot to CPE210 Connectivity but I'll need to experiment more over time.  Just FYI, I had followed my usual procedures to scan for networks, connect to it with the right password, etc.  On the Status screen it would show connected and then a few seconds later it would disconnect.  A few seconds later the cycle would repeat.  So, to re-state.  AT&T Hotspot up and running.  Tested and working using other devices.  CPE210 sees it, connects, then disconnects, repeat.  

BTW, that's not always the case.  Sometimes the CPE210 connects to the AT&T or Verison Hotspot and seems to have a good, solid connection, but I still can't get the Router network to get Internet access.  The ASUS shows no connection (red lightning bolt) to the CPE210.  That can't be completely true because I usually access the CPE210 from the 192.168.1.X network... through the ASUS router.  

Are there any tools or logs in the CPE210 that can help me troubleshoot connectivity issues?  CPE210 Traces?  I suppose I could try pinging a known Internet site from within the CPE210 but that won't help solve the problem, only isolate things a bit more.  

Thanks in advance for any help. 

Oh, and to anyone that this all makes sense to... if you've suggestions for a better way to do this, I'd love to hear it.  They make all-in-one boxes that do something like this but they're in the $500 range.  I don't mind the expense as much as I don't like the loss of flexibility.  For example I'd lose my ability to chose my Cell Vendor and I'd be locked into one.  This solution has worked for years... most of the time.  Also, I'm open to running Tomato, DD-WRT, whatever on the router.  I know this is NOT a router forum but it's an integral piece, when coupled with the CPE210.