Coach Specialists, who stores and does work on RVs near me, highly recommended Southwest International Trucks for work they couldn't do on my Sprinter. Southwest International has multiple locations in the DFW area with one in Arlington that might work for you.
If Denton isn't too far from you then you might try The Shop on I-35 just north of Camping World. A small family owned place that handles almost anything RV related. They're right next door to a diesel shop and I think the two businesses work together on issues as well.