Such a shame you paid that amount for brake replacement. If it was for two sets of Dexter axles the entire set of four new backing plate assy with brakes, new hubs, bearings, races, seals,lug nuts would have cost about $800 for twoi axles..
https://thetrailerpartsoutlet.com/pr...BoCSKIQAvD_BwE
Their labor rate must be north of $150 an hour or they are slower than molasses
Regarding your rig sitting full of water at below 20 degree temps:
.. Take a close look at that water heater to see if it is cracked or bulged
.. All PEX Fittings and lines
.. toilet pedal water valve
.. all sink and shower fixtures
.. batteries are probably completely shot
I have seen what happens out here in Idaho when folks leave their RV full of water.. A few days at 18 degree temps does an awesome job on the plumbing
..