Upon returning to my R-pod on a warm day (after multiple hard freezes) to check on it, I found a very small amount of water that puddled somewhere near the hot water heater and ran under the sink. 

Under the sink there is some sort of unit flashing red 3 times, then green once, and continually cycling through in that routine.

I pulled the anode rod and only about a half gal of water came out so I must have pushed most of the water through the system with air pressure during my terrible attempt to winterize the unit.

Before I go willy nilly buying parts and attempting to repair, I thought I would check with all you pros to see:

1) what are the most likely points of failure?

2) what will likely need replacing vs fixing?

3) what the flashing light (senser?) under the sink is?

Thank you very much for your time and responses!

will need a picture of the flashing light.. it may be a slide controller.

the "best way" to find any water damage is to pressurize the system and look for leaks. Hopefully you didn't lose the WH, they are a pain to replace. If it was mostly empty, the tank should be fine, but the lower valve and connection may be broken.

It sounds like you winterized with air.. so hook up again, pressurize to 25 psi, look and listen. If you don't find anything. Hook up to water, and again, look and listen. You may have gotten lucky.

Turns out I dodged most all damage - rather be lucky than smart, I guess.

The hot water heater and all lines were in working order. The hot/cold nobs on the outside shower busted thier seals and were leaking so I had to replace that (15 dollar part on amazon) which was probably unrelated to the way I winterized and more so just normal wear and tear. This is likely where the little bit of sitting water I found came from. Not sure about the code/fault light on the slide out, probably a low battery thing. Now that the batteries are charged the slide out works.

Thanks again and happy camping!