I'm not sure how to reply. I'm having trouble getting past the time line of events. Four years sitting and making payments the entire time? You should have been on a first name bases with someone a Workhorse after four weeks. After four months I would have paid to have the work done and then started legal action for both loss of use and the repairs. After four years I'm not sure you have much to work with unless you have very detailed documentation showing you were in near constant contact with Workhorse to have this resolved.
Workhorse was responsible for the brake problem but everything else was your responsibility to maintain. Year oil changes, semiannual roof inspection, monthly generator runs, checking tire inflation, cycling the hydraulics, battery water levels and the list goes on. The coach may well have been unsafe to operate but I not sure how you are going to justify allowing it to deteriorate to a point that it is not usable as a Workhorse related failure. The possibility of an insurance claim is equally distant. Again there is an expatiation on your part to maintain the coach.
Really sorry to read the original posting but I just can't get past the time line of events.