Take it to a frame and axle shop. They will know exactly what to do and if anything else needs attention.
The real problem with frames is that there are no design/construction standards/codes for them. Lippert can and does build them however they want and don't have to answer to anyone. You might consider sending photos to Lippert just for the record and telling them they build terrible frames. They will likely tell you it's your fault for overloading it tho.
We have our own horror story with a Lippert frame and can't talk about it.
Yes, if in the market, buy any Northwood product or one with a BAL frame like Lance. There's a few other makes/models out there with the BAL frame like the Jayco Whitehawk.