If your speakers+ amp are in an environment without WiFi, there really isn’t an advantage to using Sonos gear over regular audio gear.  You could use Sonos gear, but you wouldn’t be able to use any of the functionality that Sonos brings.

Not well.  The line-in on the older amp models has a delay and will not be in sync with your TV audio.  

You would likely set it (the new amp) up inside and then bring it outside after setup.  It should connect to your TV automatically and you would then control volume through the TV remote.

if your ipad is the hotspot, the Sonos app would need to be on a different device connected to that iPad hotspot.

I’m not familiar with water proof amps,  but they surely exist.  You can also get enclosure that help protect amps placed outdoor.   As I said before though Sonos amps don’t have any advantage over other amps for your scenario.

Google “Sonos Amp Enclosure”.  There are only a couple options, and I haven’t heard anything bad about any of them.

HDMI-ARC, as that will be the connection without any delay.

One option to try is to get a Sonos Move and connect it to the TV via bluetooth.  It’s not design for this use and you may notice a delay, but some don’t notice a delay.  You can also easily bring it in and out to the space, plus it’s IP rated, and you can use it on the go as well.

I honestly would be tempted to just get a cheap soundbar for this case, one that maybe fits under your TV cover, is loud enough for your needs, and you don’t really care much if it gets damaged.

Could this be a “connect for the evening” arrangement or do you need this to be seasonal? Is the old CONNECT:AMP compatible with the SONOS controller that you are using? (New controller needs a CONNECT:AMP with a date code of 2015 or later.)

With some effort you could extend WiFi range, but do you need an operating SONOS system out there? If not, a 3rd party amplifier in an appropriate enclosure would be a reasonable approach. Does your TV have an analog audio output?

So I bought a Sony HTS 100 Sound bar and I can barely hear it. I messed with all the Audio settings and it just isnt loud enough. 

Is there a big soundbar that may work ? 

I really love Sonos stuff but am worried its going to be a huge headache using without any Wifi…. 

TV has a headphone jack output, HDMI, and Optical Out 

With a 3rd party amplifier, voice sync will be OK unless the TV’s audio output has timing issues. Headphone jacks sometimes compromise audio quality a bit, but in your noisy environment this will not be the dominant issue. An optical to analog converter is relatively inexpensive, will maintain audio quality, but it is another “box” to deal with. With SONOS AMP you’ll have best voice sync with the HDMI-ARC connection. A benefit of using the headphone output is that the TV’s Volume control will work, the other outputs will assume that the follow-on audio system will control Volume.

Does it have bluetooth?  If so you could use headphones or any bluetooth speaker.  You can place the speaker close to you if you’re looking to improve volume.